FMFRP 0-54 the Persian Gulf Region, a Climatological Study

Home , Gulf low, Gulf of Oman, Siberian high

FMFRP 0-54

The Persian Gulf Region, AClimatological Study

U.S. MtrineCorps

PCN1LiIJ0005LFII 111)

DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited DEPARTMENT OF THE NAVY Headquarters United States Marine Corps Washington, DC 20380—0001

19 October 1990

FOREWORD

1. PURPOSE

Fleet Marine Force Reference Publication 0-54, The Persian Gulf Region. A Climatological Study, provides information on the climate in the Persian Gulf region.

2. SCOPE

While some of the technical information in this manual is of use mainly to meteorologists, much of the information is invaluable to anyone who wishes to predict the consequences of changes in the season or weather on military operations.

3. BACKGROUND

a. Desert operations have much in common with operations in the other parts of the world. The unique aspects of desert operations stem primarily from deserts' heat and lack of moisture. While these two factors have significant consequences, most of the doctrine, tactics, techniques, and procedures used in operations in other parts of the world apply to desert operations. The challenge of desert operations is to adapt to a new environment.

b. FMFRP 0-54 was originally published by the USAF Environmental Technical Applications Center in 1988. In August 1990, the manual was published as Operational Handbook 0-54.

4. SUPERSESSION

Operational Handbook 0-54 The Persian Gulf. A Climatological Study; however, the texts of FMFRP 0—54 and OH 0-54 are identical and OH 0-54 will continue to be used until the stock is exhausted.

5. RECOMMENDATIONS

This manual will not be revised. However, comments on the manual are welcomed and will be used in revising other manuals on desert warfare. Submit comments to ——

CommandingGeneral Marine Corps Combat Development Command (WF12) Quantico, VA 22134—5001 6. CERTIFICATION

Reviewed and approved this date.

BY DIRECTION OF THE COMMANDANT OF THE MARINE CORPS

M.P. CAULFIELD Major General, U.S. Marine Corps Deputy Commander for Warfighting Marine Corps Combat Development Command Quantico, Virginia

DiST: 1L100005L4000

2 PREFACE

This technical note documents and consolidates work done to complete USAFETAC Project Number 703-30 for 5WW/DNC, Langley AFB, VA 23665-5000.The project leader was Capt William F. Sjoberg, USAFETAC/ECR. Lead researcher and writer was Mr Kenneth R. Walters, Sr., USAFETAC/ECR. USAFETAC's Operating Location A at Asheville, NC made a major contribution in providing special data summaries.The authors are indebted to Mr Keith Grant of the British Meteorological Office for his out- standing cooperation and many contributions of data.Companion documents to this work provide detailed electrooptical transmittance climatology and refractivity data for the Persian Gulf region;see USAFETAC/TN-88/003, Persian Gulf Transmittance Study, and USAFETAC/TN-88/004, Persian Gulf Refractivity Study.

CONTENTS

Page Chapter 1 INTRODUCTION. 1 Area of Interest.,,,,,.,,,,,. 1 Study Content 1

Climatological Regimes 1 Conventions I Data Sources 1 Related References I

Chapter 2 PHYSICAL GEOGRAPHY 3 Naps and Charts 3 The Persian Gulf 3 The Iranian Shore 3 The Northwestern Shore.,,., 3 The Southern Shore 3 The Strait of Hormuz 3 The Gulf of Oman 3 The Iranian Coast 3 The Onani Coast 3 The Ornani Arabian Sea Coast 3

Chapter 3 THE MONSOON CLIMATE 5 The Monsoon Defined.,,,,,,,,.,,,,,,. 5 Seasons of the Southern Asia Monsoon 5 The Northeast Monsoon.,,.,, 5 The Spring Transition,,,,,. 5 The Southwest Monsoon., 5 The Fall Transition..,, 5 Tropical Storm Formation., 5

Causes of the Monsoon S

Chapter 4 THE NORTHEAST MONSOON 6

Semipermanent Climatic Controls,.,.,,,. S The Mediterranean Storm Track,,,,,,, 6 The Persian Gulf Trough 5 The Saudi Arabian High 5 Northerly Airflow Cocnponent,,...,.,,... 7 The Siberian High 7 Arabian Peninsula/Iran Upper—Air Ridge. 7 The Polar Jet Stream.,,.,.,..,,,..,,.,. 7 The Subtropical Jet Strean 7 Warm Persian Gulf Waters...,,,,. 7 Transitory Synoptic Features 13 The Ornani Convergence Zone (OCZ) 13 Surface Cold Front/Strong Upper-Level Troughsin the Westerlies, 13 Surface Cyclogenesis 13 The Persian Gulf Proper and Adjacent Land Areas., 15 Mesoscale Synoptic Features 15 Typical Weather 15 Sea Surface Conditions 21 The Strait of Hormuz 22 Mesoscale Synoptic Features 22 Typical Weather 22 Sea Surface Conditions 22 The Gulf of Oman and Adjacent LandAreas 23 Mesoscale Synoptic Features 23 Typical Weather 23 Sea Surface Conditions 23 The Reani Arabian Sea Coast,.,.,,,. 24 Mesoscale Synoptic Features .24 Typical Weather .24 Sea Surface Conditions,,,.,,,,,. .24

iii Chapter 5 THE SPRINGTRANSITLON .25 Major Climatic Controls .25 Flow Pattern Reversal Strengthening Continental Low Pressure Centers .25 The Upper-Level (Above 300mb) Subtropical Ridge.... .25 Interaction Between the Polar and Subtropical Jets. Mean May Flow. .25 Transitory Synoptic Features .29 Tropical Cyclone Frequency . .29 Tropical Storms .29 The Onset Vortex .30 The Desert Front .30 The Omani Convergence Zone (OCZ) .30 Land—Sea Breezes .30 The Persian Gulf and Adjacent LandAreas.. .31 Mesoscale Synoptic Features .31 Typical Weather .31 Sea Surface Conditions .32 The Strait of Hormuz .33 Mesoscale Synoptic Features .33 Typical Weather .33 Sea Surface Conditions .33 The Gulf of Oman and Adjacent LandAreas.. .34 Mesoscale Synoptic Conditions... .34 Typical Weather .34 Sea Surface Conditions .34 The Onani Arabian Sea Coast .35 Mesoscale Synoptic Conditions... .35 Typical Weather .35 Sea Surface Conditions .35

Chapter 6 THE SOUTHWEST MONSOON REGIME 36 Major Climatic Controls 36 A Massive Thermal Low—Pressure Trough 36 An Upper—Air Ridge 36 The Monsoon Trough/Intertropical Convergence Zone (ITCZ) 36 The Southwest Monsoon 37 Strong Upwelling 37 The Tropical Easterly Jet (TEJ) 37 TwolrnportantAirflowFeatures 37 Mid—Level Moisture 37 A Persistent Mid—Level Trough 37 Extremely Warm Persian Gulf Waters 37 Mean July Flow 37 Transitory Synoptic Features 41 Weak Upper—Level Troughs in the Westerlies 41 Northwestward Movement of the Monsoon Trough/ITCZ 41 The Onset Vortex 41 Tropical Cyclonic Storms/Cyclones 41 The Persian Gulf and Adjacent Land Areas 42 Mesoscale Synoptic Conditions.. 42 Typical Weather 43 Sea Surface Conditions 45 The Strait of Hormuz 46 Mesoscale Synoptic Conditions... 46 Typical Weather 46 Sea Surface Conditions 46 The Gulf of Oman and Adjacent LandAreas. 47 Mesoscale Synoptic Conditions... 47 Typical Weather 47 Sea Surface Conditions 48 The Ornani Arabian Sea Coast 49 Mesoscale Synoptic Conditions... 49 Typical Weather 49 Sea Surface Conditions 49

iv Chapter 7 THE FALL TRANSITION .50 Major Climatic Controls .50 Flow Pattern Reversal .50 Weak Low—Level Continental Anticyclones.. .50 Strong Upper—Level Westerlies . .50 Mediterranean Cyclones 50 A Weak Mid—Level Trough 50 The Monsoon Trough/Intertropical Conyergence Zone (ITCZ) 50 Tropical Cyclones 50 Semipermanent Sudan Low 50 Mean October Flow SO Transitory Synoptic Features 54 Weak Upper—Level Troughs 54 "Winter Shamals" 54 The Persian Gulf and Adjacent Land Areas 55 Mesoscale Synoptic Conditions 55 Typical Weather 55 Sea Surface Conditions.....,,,.,,,,,. 55 The Strait of I4ormuz 57 Mesoscale Synoptic Conditions,,,,.,,, 57 Typical Weather 57 Sea Surface Conditions 57 The Gulf of Onan and Adjacent Land Areas 58 Mesoscale Synoptic Conditions 58 Typical Weather 58 Sea Surface Conditions 58 The Omani Arabian Sea Coast Mesoscale Synoptic Conditions...,,.,, Typical Weather 59 Sea Surface Conditions 59

B IBLIOGRAPHY' .60

V FIGURES

Figure 1. Topography of the Persian Gulf Region .2

Figure 2. Delineation of the 'Monsoon Region' • 4 Figure3. MeanWinterStormTracks .6 Figure 4. Typical Northeast Monsoon Surface Analysis .8 Figures. Typical Northeast Monsoon 500mb Analysis,,,,,,,,,,. .9 Figure 6. Mean January 850mb Flow .10 Figure 7, Mean January 700mb Flow .10 Figure 8. Mean January 500mb Flow .11 Figure 9. Mean January 300mb Flow .11 Figure 10. Mean January 200mb Flow .12 Figure 11.Mean January Position of the 007 .13 Figure 12. Representative Surface Chart for 24—36 Hour Shamal(1200Z 24 January 1973) .16 Figure13. Representative 500mb Chart for 24-36 Hour Shamal (12007 24 January 1973) 17 Figure14, Representative Surface Chart for 3—5 Day Shamal Surface Chart (00007 17 January 1973)...18 Figure15. Representative 500mb Chart for 3-5 Day Shamal (00007 17 January 1973) 19 Figure16. Areas of Stronger Shamal Winds 20 Figure 17 Mean May 850mb Flow 26 Figure 18. Mean May 700mb Flow 26 Figure 19. Mean May 5DOmb Flow 27 Figure 20. Mean May 300mb Flow 27 Figure 21. Mean May 200mb Flow 28 Figure 22.Mean Tropical Storm Tracks—-April and May Combined 29 Figure 23.Mean Position of the Desert Front 3D Figure 24.Mean April Position of the OCZ 30 Figure 25.Mean July Surface Position of the Monsoon Trough/ITCZ 36 Figure 26.Mean Winds, Temperatures, and Geopotentials-—Salalah, 12007, July 1980 37 Figure 27.Mean July 850mb Flow 38 Figure 28. Mean July 700mb Flow 38 Figure 29.Mean July 500mb Flow 39 Figure 30. Mean July 300mb Flow 39 Figure 31.Mean July 200mb Flow 40 Figure 32. Mean Tropical Storm Tracks——June 41 Figure33. Low—Level Wind Profileover8ahrain 42 Figure34. Percentage Frequencies of Visibilities—3MM, Bahrain 43 Figure35. Percentage Frequencies of Visibilities—1,100 Yards, Bahrain 44 Figure36 Mean Tropical Storm Tracks-—October and November Combined SD Fig ure37. Mean October 850mb Flow 51 Figure38. Mean October 700mb Flow 51 Fig ure39. Mean October 500mb Flow 52 Figure40. Mean October 3ODmb Flow 52 Figure 41. Mean October 200mb Flow 53

vi Chapter 1

Ih'TROI%XTION

= ==

AREA OF INTEREST. Thisstudydescribesthe DATA SOURCES, The authors used a number of United climatology of the Persian Gulf, the Strait of States andforeign climatologicaland meteoro- Hormuz,theGulf ofOman, andtheiradjacent logical studies from the collections of the Air landareasfor aradius of 150MM, Land areas Weather ServiceTechnicalLibrary (AWSTL) as include portions of Iran, Iraq, Kuwait, Bahrain, well assi.anmarizeddatafrom theAir Weather the United Arab Emirates, and Oman. Service Worldwide Climatic Database, An extensivebibliographyisprovided. As the STUDYCONTENT. Chapter 2 describes geography in reader willnote, there are many other excellent the areas of interest. Chapter3 discusses the studies on the climatology of the Persian Gulf phenomena of the monsoon climate as it affects region--notablythe AWS 100-seriesForecaster thePersianGulf region, Subsequent chapters Memos (FM5) and at least one 'Follow—On (onefor each of the four 'seasons"or clima— Training' slide/tape module. Forecasters tological regimeslisted below) describethe interested inthisregionshouldacquireand "semipermanentclimatic controls'and"transi- become familiar with ct least the following: tory synopticfeatures' conmiontoeach of the fourseasons, "Mesoscalesynopticfeatures," • NEPRFContractorReport83-06,Forecasters' "typicalweather," and'sea surface conditions' Handbook for the Middle East/Arabian Sea, AD- arethen discussed for each seasonin each of A134312. four major geographical subdivisions (the PersianGulf proper, the. Strait of Hormuz, the • NEPRF TechnicalReport83-03,Navy Tactical Gulf of Oman, and the Omani Arabian Sea Coast) Appl icat ions Guide, Volume 5,Part 1:"Indian that make up the entire Persian. Gulf region, Ocean Red Sea/PersianGulf WeatherAnalysis and Forecast Applications,' AD-A134412. CLIMATOLOGICAL REGIMES. Thefour climatological regimes(or"seasons")describedherearethe • NEPRF Technical Report 79-06, Winter Shanialin same as those usedin t.he "Forecasters' Handbook the Persian Gulf, AD—A077727. for the Middle East/Arabian Sea" and are further discussed in Chapter 3, They are: • "Terminal Forecast Reference Notebook,' USCENTAF ELF One. •The Northeast Monsoon (December—March) RELATED REFERENCES. Station Climatic Swrrnaries-- SThe Spring Transition (April—May) Asia (USAFETAC/DS-XX/O35), published by the USAF Environmental Technical Applications Center •The Southwest Monsoon (June—September) (USAFETAC) , gives standard weather station surmuariesfor specific locations inthe Persian SThe Fall Transition (October—November) Gulf area;the latest version. of this document is available from the Defense Technical Information Center (OTIC) . 000 users may order CONVENTIONS, The spellings ofplacenamesand through AWS staffweatherofficersordirect geographical featuresarethose used by the from: AWSTL, FL4414, Scott AFBIL 62225-5458. UnitedStatesDefense Mapping Agency Aerospace Detailedelectrooptical and refractivitydata Center (DNAAC) , Distances are innautical for the Persian Gulf region are available in two miles. Elevations areinfeet with a meter (m) companion works to this study: orkilometer(km)valueininediately following, TemperaturesareindegreesFahrenheitwitha • USAFETAC/TN-88/O03, Persian Gulf Transmittance Celsius conversion (°C)following. Wind speeds Study in the 8-12 Micron Band are inknots. Precipitationamountsarein inches, with a millimeter (em) conversion • USAFETAC/TN-88/004,Persian Gulf Refractivity following, Study.

1 I

4) I

•1.

2 Chapter 2

PERSIAN9/IF OGR4 IWV

====

NAPS AND CHARTS. Figure 1 shows thegeneral the middleof the mouth ofthe Gulfof geographyand topographyofthePersianGulf Bahrain, Terrainin Saudi Arabia inland of the region. For more detail ,readers are urged to shoreline is a mixture of sand dunes, wadis (dry acquireand useDMAAC navigation charts. The washes), and lowgravelridges. Sanddune TacticalPilotageChart (TPC) andOperational fields are concentrated within 5ONM of the coast Navigation Chart (ONC)seriesare recommended. from Kuwait to Dhahran; south of Ohahran these Note that weather stations in Iran and Iraq have fields extend inland from 75 to ZOONM, transmitted virtually no weather data since the Elevationsriseslowlyinlandtoabout1,700 start of thefran—Iraqwarin1980. Readers feet (520m). South of Abu Ohabi, and extending should consult the current version of the 'AWS southwesttothe mountains of extreme eastern Master stationCatalog"forthemostrecent Yemen, is the 'Empty Quarter."There are almost weather station information. no permanent human inhabitants here in the sand dunes and ridges.In the Oman Peninsula the sand THE PERSIAN GULF itself extendsin a great 530 dune fields become mixedwith sand ridges. nauticalmile concavecurve fromthe Shatt These extend south and eastward to within 50 to al'Arab (Euphrates River) delta to the Strait of 75NM of the mountainrangealong theGulf of Normuz. Widths from the Shatt al'Arab toAbu Oman-Arabian Sea coast. Salt flats are common Ohabi averagebetween I3ONM to a littleover within 15MM ofthecoast alongtheentire 1SONM. Eastof Abu Ohabi,thegulf narrows southern gulf shore, rapidly to JONM just east of Dubai.Gulf waters are relatively shallow——average depthvaries THE STRAIT OF HORMUL. At Oubai, the Persian Gulf from 65to 200 feet (20 to 60m) , Deeper waters beginsits rapidnarrowingintotheStrait of occur only on the immediate western side of the Flormuz. Although thestrait averages SONM in Straitof Hormuzwhere depths reach300 feet width,thenarrowestpartisslightlyunder (90m). 30MM. Depth averages from 130to 260 feet (40 to 80m) The Iranian Shore. Terrain ontheIranian, or northern, shore of the Persian Gulf is in sharp THE GULF OF OMAN extends south and then contrasttothe rest of the region. Numerous southeastward from the Strait of Hormuz into the mountain ranges, oriented parallel to the Arabian Sea. The generally accepted boundary Persian Gulf—Gulf of Oman, front a narrow (20 to between the Gulf of Oman and the Arabian Sea is 4ONM) coastalplain fromtheTigris—Ehprates an imaginary line drawn from Jiwani on the Iran— deltasoutheastwardfor105MM or to just under Pakistan frontier south—southwestwardtoRas al 2ONM southeast of Bushehr, Southeast and east Hadd——the easternmostpointof Oman. Widths of this point to the Strait of Hormuz, the major rapidly increase from 30MM at the eastern end of ranges rise almost immediately inlandfrom the the Strait of Hormuz to 130MM wide at Muscat and coast, The highest mountains are inland of the finally to 200NMwhere it joins the Arabian Sea, northwestern half of the gulf; here, numerous peaksrangefrom 11,000feet(3,355m) to more The Iranian Coast,From the Strait of Hormuz to than14,000feet(4,270m). The highestpeak theIran—Pakistan border, mountain ranges form reaches 14,465 feet (4,410m)in the Kuh—E Dinar the coast andrise rapidly, Narrow (10—15MM) range near 30°57'N, 51°26'E. plainsarelocatedaroundthemouthsofthe rivers flowing into the Gulf,Elevations within TheNorthwesternShore. Saltmarshesatthe 4ONM of the coast exceed 5,000 feet (1,525m); northwestern end of the Persian Gulf extend from within 90MM, peaks exceed 10,000 feet (3,O48m). Kuwait to the Iranian coast near 30°N, 50°09'E, and inland from 15 to 7ONM.The greatest inland The thiani Coast.A range of mountains runs the saltmarshpenetrationisbetweenKuwaitand lengthof Oman fromJazireh—al Ghanam inthe Bandar-E Mahshahr, where they reach almostto Strait of Hormuz to 20MM west ofRasalHadd, Basrah, Except foriimiiediateriverbanks, Elevations range from 5,000 to 9,000 feet (1,525 desert lies beyond thesalt marshes. Most of to2,745m). The highest known elevationis these desertsare covered witha top layer of 9,777 feet(2,980m)intheJabalAkhdar range fine, powdery soil that serves as the source for near 23°14'M, 57°17'E. There is a narrow (15 to major dust and sand storms. 30MM) coastalplain between Shinas and Muscat. To the west of this mountainous spine, The Southern Shore is nearly flat from the Shatt elevations are less than 1,700 feet (52Dm). al'Arabsoutheastwardtothe On*ani Peninsula. The shoreline itselfis smooth, the only TheOnaniArabian Sea Coast. A narrow (10-20 exception being the Qatar Peninsula on the east mile)coastalplainisbacked byhilly,some- shoreofthe Gul ofBahrain, Al Khubar timesmountainous,terrainalongtheentire (Khobar) , the siteof Dhahran International coast. Maximum elevationsreach2,500feet Airport,marksthewestside of this narrow, (760m) elongated indentation.Bahrain Island lies in

3 Figure 2. Del meat Ion of theftnsoon Region(fna Ravage, 1971). Khromov (1957) defined a "monsoonal" area as one with opposing seasonal wind flow. In thissimplisticdefinition, Khromov ignoredthe requirement that monsoon winds blow steadily from a seasonal direction. The hatched areasi.nFigure 2 indicate the "monsoonal area' accordingtoKhromov'sdefinition. Klein (1957) postulatedthat "mo.nsoonal areas' must show lowfrequenciesofsurfacecyclone- anticyclone alternationsinsummer and winter. The heavyline with southward shading indicates the northern edge of the "monsoonalarea" according to Klein.The rectangle encloses (also simplistically) what isgenerally acceptedasthemonsoon region of the world. Ramage, however, qualifies this neatly rectangular expression; those quali- fications are discussedin Chapter 3. Note in the enlarged inset that Khromov's dividing line arcs across the Strait of Hormuz and separates the Persian Gulf itself from the Gulf of Oman and the Arabian Sea..

4 Chapter 3

THE MONSOON CLIMATE

THE MONSOON DEFINED. "Monsoon" istheEnglish periodof 7 to 15 daysfromthetime of the adaptationoftheArabian (and Indian) word first sustained cross—equator flow. It follows "Mausum,"the literaltranslation forwhichis either thedevelopmentof a mid—tropospheric "season." The termisgenerally appliedto vortexin the Bay of Bengal or an "onset vortex' areas where there is aseasonal reversal of the inthe extreme northern Arabian Sea,The latter prevailing winds. Unfortunately, some meteoro- moves westward to affect Oman. logical schoolsof thought haveappliedthis idea too loosely.For example, the Russians and The. Southwest Monsoon. The onset surge at the the Germans have implied that the Russian Arctic end of the Spring Transition marks the start of and Berlinhave "monsoon climates," A similar the Southwest Monsoon thatlasts from June designation,butwithmorejustification,has throughSeptember. southwesterlyflow has a been giventheUnited States Southwest by some direct affect on the Arabian Sea coast of Oman, American meteorologists.The generally accepted the Gulf of Oman, the Arabian Sea coast of Iran, definitionof a "monsoonclimate"isoneby southern Pakistan, and India. Low—level flow is ProfessorCohn Ramage oftheUniversityof sustainedsouthwesterly, Upper-levelflowis Hawaii, who provides these four criteria: sustained easterly; the TropicalEasterly Jet (TEJ) flowsacrossIndiaintoEastAfricaat (1)Prevailing seasonal wind directions 150mb, betweensummer andwinter mustchange by at least 120 degrees. The Fall Transition. InOctober and November, the Pakistani heat low collapses as days become (2) Both summerand winter mean windspeeds shorter. Cooling over Siberian Russia must equal or exceed 10 knots (3 meters/sec) reestablishes the Asiatic High pressure centers and the ITCZ migratessouthwardonceagain. (3)Wind directions andspeeds must exhibit Low—level northeasterlyflowisreestablished high degrees of steadiness. over southern Asia and the cycle repeats itself.

(4) No more than one cyclone/anticyclone TROPICAL STORM FORMATION. Tropical storms couplet occurs duringJanuary or July inany affecting the northern Arabian Sea are confined 2—year periodwithin any5—degreelatitude/ tothe spring andfalltransitions. These are longitude rectangle. the only times when the ITCZ is over the Arabian Sea between15° and25°Nand strongvertical Applyingthesecriteriato the Persia:n Gulf shears are absent-—both of which are necessary region, we find that the area south of July's for tropical storm formation. Monsoon Trough (orIntertropical Convergence Zone, ITCZ) position definitelyhas a monsoon CAUSES OF THE MONSOON. The massive circulation climate (See Figure 25, page 36). Areas north reversal referred to as the monsoon is still not oftheITCZ,althoughinfluencedby monsoonal completely understood. Its ultimate cause——the circulation, do not have monsoon climates. seasonal variation inincoming solar radiation—— is obvious.Solar radiation results in the fall SEASONS OF THE SOUTHERN ASIA MONSOON. The formation and spring decay of the Asiatic High, southern Asia monsoon in the Persian Gulf region aswellas the spring formation andfalldecay is characterized by two distinct seasons of the south Asian Low, What isstill .nknown separated by two short (30 to 45 day) transition are the threshold gradients that trigger these periods. transitions, The latest research suggests that thelate springtime combination of latent heat The Northeast Nonsoon (Decemberthrough March) released by pre-monsoonal thunderstormsover isdominated by northeasterly low—levelflow southern India, along withlatespringtime controlled by a deep Australianthermal low heating over the Tibetan Plateau, rapidly forms center and an Asiatic high-pressureregion an upper—levelhighpressure area over extreme centered over Siberian Russia.Upper—level flow northernIndiaandtheHimalayas. Thestrong issustained westerly, with the subtropical jet winter westerlycirculationis replaced by over southern Arabia eastward into India. strong sumer mid— and upper—level tropospheric easterly circulation.This circulation provides The Spring Transition. InApriland May the thesustainedoutflownecessaryforextended northeasterlycirculationrapidlybreaks down precipitation over southern Asia,In the fall, and isreplaced by thePakistaniLow pressure diminishing heavy convection over northern center and itsassociatedsecondarylows in India,combinedwithcoolingovertheTibetan Saudi Arabia and Saharan Africa. The ITCZ moves Plateau,hastheoppositeeffect. Low—level rapidly northintotheintensifying heatlows, circulationcharacteristicoftheapproaching Southern hemispheresoutheasterlytradewinds monsoon season precedes the reversal inupper— cross the Equator, recurve to become level flow. However, themonsoon has not southwesterly, and flow across the Arabian Sea officially begun until the characteristic upper— into India.The initial surge occurs within a level circulation has been established.

5 Chapter 4

THE AVRTNEAST MONSOON..

(Decarter-March)

SEMIPEmANENT CLIMATIC CONTROLS

THE NEOITERRSEAN STORM TRACK. This is the main THE PERSIANStilETROUGH, This relatively weak sourceoflowpressuresystems andcoolair semipermanent feature results from a combination during thisseason. Extensive thunderstorms of heating over the Persian Gulf and an induced andheavyrainsaccompanythemovementof a 'lee-sidetrough' resulting from the high secondary low across the Saudi Arabian pressurecentercover Iran and northwestern peninsula. Figure 3 shows mean January storm SaudiArabia, Itforms anaturalpathway for tracks representative of the Northeast lowpressurecentersmovingoutofsouthern Monsoon. TrackA,whichmovesnortheastward Iraq, Intensification andmovementontothe through Turkey into the Caucasus mountains,is Arabian Persian Gulfcoast as a transient the primary track for secondary low formation in feature often occurs as theresultof a northernSaudi Arabia—Iraq. TrackB,across combination ofthefollowingthreefactors: Lebanon—Israel—Syriainto the PersianGulf,is (1)the passage of acold front down the Gulf, normally associatedwiththe'wintershamals" (2) increasedridgingover Iran, and (3) thatwill bediscussedlater, Track C runs temporary weakeningof theSaudiArabian high across southern Egypt and the northern Red Sea pressure area. See further discussionsin the intocentralSaudiArabia, Itisassociated sectiontitled "The PersianGulfProperand with a mean jet stream positionover the Adjacent Land Masses." southernMediterraneanornorthernAfricaand often resultsInformation of asecondary wave THE SAUDI ARABIAN HIGH is centered over overthecentral Red Sea. This,theleast northwestern Saudi Arabia as an eastward activeofthethreetracks,occursinlate extension of the Saharan high pressure ridge. winter and early in the spring transition.

Figure 3.Mean Winter Stone Tracks.

6 NORTHERLY AIRFLOWCOMPOIENT. Theprevailing mean THE POLAR JET STREAM is located near 30°N. airflow component, as discussed in chapter 3, is December core speeds are 90knots. InJanuary northerly over the entire region. This it dipstolatitudes between 27and 29°N with northerly flow, however,isinterrupted by the speeds of 110 knots, then shifts back northward passage of upper air troughs and their to just above30°Nwith maximum speeds of80 associated surface low pressure areas and knots in March, Actual positions vary surface fronts/shear lines.See Figures 4 and 5 considerably; inJanuary,flowaroundthe fortypicalsurface and500mb analyses. Mean bott6m of a deep 500mblow may reachas far January flow at 850, 700, 500,300,and 200mb south as 20°N. Under theseconditions,it (5,000, 10,000, 18,000, 30,000, and 39,000 feet) merges with the subtropical jet stream, is shown in Figures 6 through 10. THE SUBTROPICAL JET STREAM. During this season, THE SIBERIAN HIGH hasitsprimaryaxisacross the Subtropical Jet flows from west to east over centralRussiaanda mean center over eastern the Arabian Peninsula. Mean position is between Siberia, Since direct northerly flow around the 25 and 28°N; at 200mb, core speeds exceed 110 southsideofthisridgeisblocked bythe knots over the Peninsula, Deep upper air lows Caucasus-, NorthernIranian, Hindu Kush,and may displace the jet south to near 2011. Himalaya mountain systems, the cold Siberian air isforcedtospillsouthwestward throughIran WARM PERSIAN GULF WATERS. By mid-January, surface and eastern Turkey intoIraq andthe northern water temperatures average 70°F (21°C). portion of the Persian Gulf, Snow cover over Althoughconsiderablycoolerthanduringthe the Zagros mountains maintains (and even Southwest Monsoon,theyareabout3°F(1.6°C) intensifies)thiscoldair,withconsequent warmer than that of the air passing over them, strengthening of downslope winds off the Zagros By April, however, Gulf water temperatures into the northeastern side of the Gulf. average 74°F (22°C)——only 1°F (0.6°C) more than the air temperature. Higher evaporation rates ARABIAN PENINSULA/IRAN UPPER AIR RIDGE. 500mb high from thePersian Gulfresult in a steady pressures centers are located over extreme northwestward flow of surface water through the western Arabia and over the Zagros mountains In StraitofHormuzinto theGulf; the current southwesternIran, At300mb, thisridgeis just west of the Strait reaches 2 to 4 knots. A displaced southward to between 20 and 22°N. counter—currentflowssoutheastwardalongthe bottom downthe Persian Gulf and outintothe Gulf of Oman.

7 THIS PAGE INTENTIONALLY LEFT BLANK

7b ___3J%f__I

G L54 u.: -\ '

4 —I P4-I-.! /J ec.),: : —J-\ D%7,V I . - /

- . __.-..;/-.

8 Ln

U-

9 25°E 40°E &0°E B0°E

0 30 N

20 N

10 °N

Figure 6. Mean January 850mb flow.

80 °E

30°N

20 °N

10°N

Figure 1. Mean January 100mb Flaw.

10 80° E

30°N

20 °N

1U°N

0°

Figure 8. Mean January 500mb Flow.

800 E

0 30 N

° 20 N

10°N

Figure 9. Mean January 300mb Flow.

11 ° 30 N

20°N

1O°N

Figure 10. Mean January 200mb Flow.

12 i'wAwslroar srworrc FEATURES

THE ONANI CONVERGENCE ZONE (OCZ). During normal Northwestern Arabian Sea Highs form in response northeast monsoon conditions, there is a tosurfacelowsthat moveintonorthern Saudi convergencezone over Oman south of the Hajar Arabia. Essentially, these highs are the 'cut- mountains, Itlies parallelto, and about 100 off'southeastportionsofthenormalArabian to 150 miles inland of, the coast of the Arabian Peninsula ridge. As the low tracks eastward or Sea, Figure 11 shows its mean January southeastward, high pressure spilling southward position. Low-levelnorthwesterly flow coming behindthecoldfrontabsorbstheindependent out ofsoutheasternand southernSaudiArabia southwestern Arabian Sea pressure center, meets the northeasterly monsoonal flow that has been deflectedinland due to strong sea breeze "Aziab is the Arabic name for the hot and dry circulation, Thiszonedoesnotexist when low—level southerly winds that blow occasionally there issouthwesterlyflow ahead of cold over Saudi ArabiainMarch. These winds occur fronts, or northwesterly flow behind. ahead of a secondary low that often results from thenortheastwardextensionoftheSudan low 50" so' that moves eastward towards the Persian Gulf as a wave on a slow—moving cold front (Track Cin Figure5) , These wildscause temperatures to risedramatically; Riyadh has reached90°F (32°C) during very strung Aziab conditions.

"Kaus"isthe localname for the southerly or southwesterlywindsthatblow over Oman,the United Arab Emirates,andthePersianGulfin advance of a surface low pressure center. These windscausethe mostextensivelow cloudand precipitation areas found during this season. Strung Prefrontal and Frontal Thunderstorms form in and near the Persian Gulf.Satellite imagery has shown conclusively that thunderstorms associated with cold front passage down the Gulf 20" N are similar to those foundin the United States MiddleWest. Thefavoredformationareafor prefrontalsquall linesis thecentral and southern Gulf. Vortex Phenomena in the form of waterspouts have been observedinthe southwestern Persian Gulf during December. Although no known reports of this phenomenon were made prior to1970,local Arabic wordsandtraditionindicate thatsuch phenomenahaveinfactoccurredinthepast. The recorded cases occurred in areas of Figure .71. (lean January Position of the OCZ. localized convergence and resultant heavy cumulusactivitybehindcoldfrontsorshear lines, SURFACE COLD FRONT/STRONG UPPER-LEVEL TROUGHS IN THE WESTERLIES. From mid-December through mid— SURFACE CYCLOGENESES. Three favored locations for March these fronts (with their associated upper— cycloqenesisinthisarea,inorderofmost airtroughs and oftenaccompanied by closed frequent occurrence, are: 500mblow centers)cross the region routinely. Occurrenceis most common when a blocking high Southeastern Iraq—Northern Persian 6u1 f, overnorthernEuroperesultsin a highspeed Secondary lows form in these regions inresponse coreinthe westerlies across the Mediterranean tocoldair advection, warm water, andairflow intoIraq. The characteristic middle and high channeling through the Iraqui and Iranian cloudsassociatedwiththesetroughsshow up mountains, notably the Lagros. well onboth visual and IRsatellite imagery, These systems are accompanied by the following The Western Gulf of Oman, Secondary lows form phenomena: hereforthe samereasons as insoutheastern Iraq and the NorthernPersian Gulf. The Transitory Saudi Arabian Highs form in response 'channeling' here, however, isthroughthe tothesubsiding air beneathupper air ridges Zagros Mountains of Iran along the northern Gulf movingacrosstheareafrom thewest. These ofOman coast andthrough theOmaniPeninsula cells break off from the quasi—permanent Saudi Mountains along the southwest side off the Gulf Arabian ridge and move eastward and of Oman. This combination of airflow southeastward acrossthe Peninsulafollowing modification induces cyclonic flow if a strong cold fronts. east—west ridge lies over Iran.

13 Northeastern Sudan—Northern Red Sea—Vestern potent but localized moisture source for SaudiArabia. A weak, invertedlow—pressure cyclogenesis here, The low then moves eastward trough stretches northward into Sudan from East as a wave on the front, Under proper AfricaduringmostoftheNortheast Monsoon conditions, this center will become the primary season. Passage of a cold front southeastward surface lowaffecting Saudi Arabia and the across Saudi Arabia, combined with its southern Persian Gulf, This locationis most associated upper-leveltrough approaching Sudan active during late winter (primarily March) and from the west, often triggers the formation of a during the spring transition as the strength of secondarylow on thefrontovernortheastern cold air outbreaks diminishes, Sudan and the Red Sea,The Red Sea serves as a

14 THE PERSIAN GULF PROPER AND A(UACEN LAND AREAS--WRIHEAST MONSOON

MESOSCALE SYNOPTIC FEATURES. The following Persistent dust and sandstorms on the scale of features are commonto the Persian Gulf proper the Southwest Monsoon normallyoccuronly and its irwrmediatelyadjacent land areas: during these events. A detailed explanation ofthis phenomenon, including forecasting Gulf Cyclogenesis.Cold frontal stagnation in the technique,is giveninNEPRF Technical Report southern Gulf resultsincyclogenesis northwest 79—06, Winter Shamnal inthePersianGulf, ofthe Omani Peninsula—UnitedArabEmirates, Figures 14and15are representative surface This occurs when the associated upper—air trough and 500mb analyses of the 3—5 day shareal, slowssharplyor becomes stationaryinthis area. Formation of a cutoff low at the base of ThePersianGulf Troughintensifiesinorjust the upper-air trough enhancesit. Development northeastof thePersian Gulf after a low and is rapid over the warm Gulf water, Under such its associated frontal system passes the Strait conditions, strong low—level winds build of Hormuzresultinginhigh pressure building rapidly, Wind directions shiftfrom southto over Iran,These troughs maintain stronger than southeast to northeast, and finally to normalwinds overtheSaudiArabianshore and northwest,asthelow moves through the Strait downs lope winds on the Iranian coastthat of Hormuz into the Gulf of Oman,Precipitation, reinforce normal nocturnal downslope land along with extensive low, middle, and high cloud breezes, If theIranian high pressure cellis layers, occur on both sides of theGulf. The extremel ywell developed, conditions similar to greatest extent and precipitationintensity the'Bora"of theYugoslav Adriatic coast can occurs on the Iranian side.Moderate turbulence develop. Data on maximum downslope wind speeds and icing are found over both the Omani Isnot available,butdynamicandtopographic Peninsula and the Iranian shore. considerations indicate that speeds better than 50 knots over and just offshore of the immediate The Winter Shamal,"Shamal" is an Arabic word for Iranian coast are possible, Recent ALPEX 'north." It refers to the strong northerly and researchsuggeststhatonly a shallowlayer northwesterly winds that occurinthePersian iiwaediately above the ridges accelerates; air Gulf and over its ininediate land areas following betweenthetopofthisshallowaccelerated passage ofcoldfrontssoutheastward, The layer and theundisturbedhigherlevelwind Shamal producesthemostwidespreadhazardous fieldisslow movingandextremely turbulent. weather knowntothis region,. Its causes are Under the synoptic circumstances described similar to thosefor the strong northerly winter above, conditionssimilartothose found in winds atTravis,McClellan, Mather, Beale, and ALPEX research might occur over and Castle AFBs, and NAS Lemoore inCalifornia's southwestwardoftheZagrosintothePersian Central Valley. Large pressure gradients Gulfnortheastofthe PersianGulfTrough. developbehindcoldfrontal passages due to Weakening of the Iranian High and/or the Persian upper—levelsubsidence rapidly building surface Gulf Trough ends the severe downslope wind, or highpressureoverwestern Saudi Arabia and "Bora.' Persian Gulf Trough strength normally Iraq, The strong northwesterly low—levelwinds decreases rapidly within24to48 hours after arethenquicklyreinforced by northwesterly frontal passage through the Strait of Hornruz and upper level winds behind themiddle level marks the end of the 'Shamal trough. Shamals hereare of two types:

The 24-36 How Shainal. These begin with the TYPICAL WEATHER. The following weather conditions passageofthefront. When the associated may beexpectedintheimmediatePersian Gulf upperairtroughsarerapidlymovingshort area during the Northeast Monsoon: waves, winds die after 24 to 36 hours; hence the name. Such cases are relatively common, GeneralSensibleWeather. With no uoper—air occurringtwo orthreetimes a month during troughs and associated fronts over this region, the Northeast Monsoon season.Winds typically theonlysensible weatherconsistsofhigh reach 30to 40 knots. Figures 12 and13 are cloudsoverthePersian GulfandtheArabian representative surface and 500mb analyses of Peninsula. Skies are often clear, but fog can the phenomenon. reduce visibilities in coastal regions. Radiational coolinginthe relatively moist air The 3—5DayShamal. Occuring onetothree near the water willcause fogto develop after times a winter, this phenomenon produces the sunrise; visibilities remain between 2 and 3 strongest winds and highest seas foundin the miles wellinto the morning. Patchy stratus is Gulf. OverexposedGulfwaters,sustained found during thelatenightand early morning winds reach50 knots and produce 12— to 15— hours along and just inland of coasts. Favored footwaves, This shamal arisesfromthe locationsareshallow marshy areas——mostly at temporary stagnationof a 500mb shortwave the head of the Gulf around the Shatt A1'Arab—— over or just east of the Strait of Hormuz, or and along the United Arab Emirate coastlinein fromtheestablishment of a mean longwave theextreme southernGulf. Exceptinthis positioninthe same area. Ineither case, coastal fog, visibilities are normally good, the result isa strong northwesterly surface wind that continues for 3 to 5 days.

15 ;

I I —t—.—-$.——t——.. I I 0 4 I I 4 I •—q— .p.

. s S U I I I,/ —--— —, 4 III

4' a I a

" / ' i..'m1 1uI'I

a I ,1) :.)

16 en

It A en

17 ___ _

-, N N

o—y. -____—- -g-:7 -f-(

- t — Ii--4-& II •'.,._ -I (-ti -;-v'k. WI \iN 7 ' ii-I''r- I- /I I_.I._/ I .i- \_I • L-

0 00 ::\— çj

18 e0 (.41 U) 0 U, 0 U)

-S 0 U, -I

40 L 0(.4 U,...

4.0

(.1 I U) / 0 / 0. LU / 2 0,,' 0 0 'Ir U) I (.4 Is, 1 (0 (0 F.. 'S. In U) In

19 Sky Cover. Well—developed high and middle cloud decksareassociatedwithupperairtroughs. Light to occasionally moderateicing occursin these decks above the 7,000 to 9,000 foot (2.1 to2.7 km) freezinglevel. Low cloudswith 1.000to1,500foot(300to 450 m) ceilings occurintheinwediateareaofthePersian Gulf. These low clouds advect westward around the north side of low pressure cells moving down the Persian Gulf. They can extend inland over Saudi Arabia as far as Riyadh, Low clouds normally clear within 4 to 6 hours after frontal passage. However,whenappreciable rainhas fallen, cold air stratocumulus will form for 1 to 2 days after frontal passage. In the absence ofstrong post—frontal surface winds, fog forming in those coastal areas near the head of the Gulfwill persist throughout for the daylighthoursforthefirst 24to 48 hours after frontal/trough passage. Dust, Widespread dust that restricts visibility toless than3 miles normally occurs with the firstfrontal passageoftheseason. Light precipitationduring the winter binds soil particles together; winds above 25 knots are neededto raise dust, Visibility fluctuations Figure 16.Areas of Stronger Shasta! Winds. occur as a function of low—level wind speed--the strongerthewinds,thelowerthe visibility, Visibilities can go as low as 50 meters Gulf due to the channeling effects of the Zagros inmiediately after the first frontal passage, at Mountains. There is no datathatprovides the height of a very strong 'Shamal," or with an verticalprofiles,butdynamicconsiderations "Aziab,' described below. Dust with indicate that core speeds may approach 50 knots northwesterlyornortherlywindsisinitially 1,000to2,000feet(305to610m) above the picked up from the Iraqi deserts to the surface along and just offshore of the Iranian southwest and west of Basrah, During March, an coast, Sustained strong northwesterly winds——30 'Aziab"(a hot and dry southerly wind) precedes to 50 knots——occurwiththe'wintershamals' a secondarylow movingeastwardintocentral that will be discussed later. Saudi Arabia. Dust associated with an'Aziab' comes fromthe "Empty Quarter,"orextreme Thunderstorms--often severe—-occur along cold southernSaudiArabia. By March,almostno frontsaswellasinprefrontalsqualllines precipitation has fallen over these areas,and that formoverthenorthernGulffromlate most of the area is dry sand once again, December through early March; satellite imagery isextremely usefulfor locating them. Cloud Windsaregenerallynorthwesterlyat 10 to 15 basesare relatively high, averaging 4,000 to knots over the northern half of the Gulf. Winds 5,000 feet(1.200to1,500 m)except over the over the southeastern half reflect the west-to- PersianGulf. Topsoftenexceed 40,000feet east orientation of the mountains on the Iranian (12.2 km) and tops of 50,000 feet (15.2 km) have shore. The south-to—northalignmentofthe beenreported. Surfacehail andgusty winds mountains on the Omani Peninsula of the Arabian near 50 knots have also been reported. As in coast combine withtheseotherfeaturesto the United States, severeicing and turbulence 'turn" the prevailingwinds——firstwesterly, are associated with these storms, thensouthwesterly,finallysoutherly——asone approaches the Strait of Hormuz from the west. Precipitation on theArabiansideoftheGulf Speeds decrease to 5 to 10 knots. Land and sea averages 2 to 3 inches(50to 75mm) a year; breezecirculations,ofcourse,modifythis almostallduringthisseason andalmostall pattern. There are two areas with winds from thunderstorms. There isconsiderable significantly higherthanthose observed along precipitation variability; some winter months theArabianPeninsulacoast (SeeFigure16). may receive more rainfallthan the mean yearly During December and January, theareajust totals."Kaus" winds ahead of the storm systems northeast of the Qatar Peninsula sees speeds 10 mentionedabove resultinextendedperiods of to15 knots higher than at Dhahran or Bharain, lowcloud and drizzleoverthemiddle and InlateFebruary andMarch, the area just off southernPersianGulf,theIraniancoast, and the Iranian coast near Lavan Island east— the southern Zagros Mountains, Such flow northeastofQatarhaswindsIDknotshigher usually occurs ahead of a low center moving down thantherestof thearea. Southwesterly or the Gulf, Higher elevations see thunderstorms southerly low—level high speed wind maximums, or and steady rain rsulting from forcedlift up 'lowleveljets'(LLJ5) ,occur aheadoflow the mountain slopes. Increased icing as well as centers throughout the area, LLJ5 are moderate mechanicalturbulence arefound along reinforced over the eastern side of the Persian the Iranian shore and over the mountains, The

20 effectsofthesewinds can be seen inthe west side of the Omani Peninsula to join fresh precipitationtotals--4to 5 inches(100to Gulf ofOman water entering through the Strait 125m)a year, or 60% higher than on the Arabian of Hormuz, Mean speeds are less than 1 knot, sideoftheGulf, The areaaroundBushehr Maximum calculatedspeedfor a 100—year worst receives almost13 inches annually——5 inches in case of combined wind and tidal currents, was 8 December alone. As on the Arabian coast, there knots at ,Jubail,As water increases in density. islarge variability; soee wintermonths itsinks,movessoutheastward, andflows back receive more precipitationina month than the intotheGulfof Oman as a bottomcurrent mean yearly totals, through the Strait of Hormuz.85% of all wave heights average less than 6 feet in the western AirTemperature. Daytime maximumtemperatures Persian Gulf, Predominant directions along the along the Imediate coast average between 65 and Arabian coast are,as mightbeexpected,from 15°F(19and 23°C). Inland, temperatures rise 330 through 360 degrees, However,underthe to70to 85°F (21to29°C) , Minimum tempe!-a- influence of a "24to 36 Hour Shamal ,'waves M3 tures along the coast fallto 45 to 65°F (7 to routinely reach 8to 10 feet; for a to5 Day 19°C). Despitethe warm Persian Gulf waters, Shamal," heights reach 12 to 15 feet. The usual dew pointsalongevehtheimediatenorthern 'decay time" to reach the normal6 foot heights coastline range from 30°F (-1°C) to 40°F after the ending of a"Shamal' varies from 6 to (3°C). Thesouthern Arabian coasthas higher 18 hours, depending on the duration and strength dewpoints--55to60°F(13°to 16°C)—-dueto of the "Shamal," 'Kaus" winds will establish a winds coming directly off the water,Dew points 6 to 8 foot southwesterly wave; greatest heights droprapidly as one moves inland from the arefoundalong the Iranianshore. Note that irmeediate coast, Riyadh averages a 30°F (—1°C) theseare 'openwater" waves;oil companies dew point through the winter. Minimum operating in the Gulf have reported higher waves temperatures drop accordingly. Beyond 20 to30 iermediately offshore during favorable miles inland, minimum temperatures drop to 35 to conditions. 45°F (3to7°C). Dew points,however,rise rapidly when a'Kaus" windisblowing. Riyadh has reported risesto59 or 61°F(15to16°C) Water Temperatures. Inthe shallow waters of the just before passage of a cold front. Gulf, temperatures cool rapidly during late fall and earlywinter. Surfacewatertemperature ranges from 72—76°F (21-24°C)in Oecember to 66- SEA SURFACE CONDITIONS, Persian Gulf. 72°F (18—22°C)in February before rising to 68— 74°F (20-23°C) in March. Temperatures in Water currents inthe Persian Gulf have a general extremelyshallowcoastal watersreach60°F counter—clockwise circulation, A steady flow of (15°C) in January. Available temperature surface water enters the Gulf through the Strait soundingsinthewesternPersianGulfshow a ofHormuz, Thissurface currentflows toward bottom temperature of 61°F (16°C) at 60 thewestandthennorthwest as ithugsthe meters, Temperatures show asteady and gradual Iranian shore.At the northern end of the Gulf, decreaseintemperature between the surface and itturns southeasterly toparallelthe Arabian the bottom of about 5°F (3°C).Thermoclines are coast.Finally, it turns northerly along the not evident.

21 THE STRAIT & NO1J(UZ--M1RTHEAST MONSOON

NESOSCALE SYNOPTIC FEATURES. Thefeaturesthat the Omani shore, gusts reach 30 to 35 knots. As affect the Persian Gulf proper and its adjacent the 'PersianGulfTrough" forms and moves land masses also affect the Strait of Hormuz. southwestward across theGulf, downslope winds blow off theIranian coast. Strong winds are rare and normallyconfinedtothestrongest TYPICAL WEATHER. The following weather conditions stages of a '3 to 5 Day Shanal may be expected in the Strait of Hormuz and its iumiiediately adjacent land areas: Dust. Almost always advected from Saudi Arabia or Iraq,dustisnormally confinedtothefirst General Sensible Weather. Sensible weather over coldfrontpassages of theseason, However, the Strait during the northeast monsoon season southwesterly flow lateinthe season ahead of normallyconsistsofpatchy lowstratus and developinglowpressureareas,eitherinthe stratocumulus, occurring most frequently during PersianGulforincentralSaudiArabia, may late evening and earlymorning, Onshore bring blowing dust orsand into the Strait of cloudiness occurs only along the Iranian coast Hormuz from the Saudi Arabian "Empty Quarter." as a function of land—sea breeze circulation. Such occurrencesrarelylastlongerthan 12 hours. Sky Cover. Well-developed high and middle cloud decksareassociatedwithupper—airtroughs. Thunderstor.soccuroverthemountainsonboth Ceilings range from 7,000 to 9,000 feet (2.1 to sides of the Strait, but are confined to areas 2.4km). Lower ceilings——1,000 to1,500 feet imediately preceding, and with the passage of, (300 to 425 m)-—normally only occur just coldfrontsoruppertroughs, Some maybe preceding or in the imediateareaoflow severe. Tops oftenexceed40,000feet(12.2 pressure centers. Light or occasionally km) ; severe thunderstorm tops have been moderate icing and turbulence occur above 8,000 reported above 50.000 feet (15.2 km). to 10,000 feetjust aheadof and withthe Prefrontalsquallline thunderstorms tend to be passage of upper troughs or sur lace low pressure strongestovertheOmani Peninsula; embedded systems and their associated fronts, Icing and pre—warm front thunderstorms are strongest over turbulence are stronger over the Omani Peninsula the Lagros Mountains on the Iranian shore. Most and Iranian mountains. embedded thunderstorms are associated with southern Persian Gulf cyclogenesis. Winds. Low—levelairflow reflects a combination of: (1) weak outflow from the Persian Gulf, Precipitation. Lightrain,rainshowers, and (2) pronounced land—seabreezes(especially occasional thundershowers occur with low alongtheIranianshore) ,and(3) a general pressure areas, cold fronts, and upper troughs, northerly to northeasterly flow off the Iranian The greatest amounts fallon the Iranian side, coast. Complicating this pattern is the As with the rest of the region, precipitation Is terrain—induced venturi effect. Although extremely variable, While Bandar Abbas averages precisedata forthe Straititselfisnot 4.7 inches (12Dm) during the winter, some years available,it appears thatin the absence of a see no rain at all and others have seen as much dynamic surface low or 'Shamal ,' wind speeds are as 13.2 inches (335m), determinedbylocal land—seabreeze relation- ships and terrain peculiarities. AirTemperature. Maximum temperaturesaverage from 70 to 85°F (21 to 29°C); minimums from 55 Winds along the northshore of the Strait are to 65°F (13to 18°C). Temperatures inland are northeasterly toeasterly duringthe nightand modified byincreasedelevation and the sea early morning, and southerly to westerly during breeze. late morning and afternoon.Along the southern shore andundersimilar conditions, winds are southwesterlytowesterly eastofthe:Strait SEA SURFACE CONDITIONS. Strait of Hormuz, during the night and early morning, and southeasterly to southerly west of the Strait. Water Currents. Flow through the Strait consists Speeds average 3to 7knots. Late mornings and of tidal ebb and flood. During ebb conditions, afternoons have pronounced sea breezes that are currents of less than 1 knot flow predominantly southwesterly to west—northwesterly west of the from thePersianGulf through theStrait into straitand northerlytonortheasterly eastof the Gulf of Oman, During flood tide, currents the strait. Sea breeze speeds reach 12to 20 ofless than 1 knotflowintheopposite knots. direction,fromtheGulf ofOman through the Strait into the Persian Gulf. 85% of all wave During 'Shamal" conditions, low—level winds turn heights average less than 4 feet (1.2 meters), westerlytowest-northwesterly approaching the Strait. Windspeeds overthe Strait andalong Water temperatures are similar to those foundin theIranianshorereach 25 to 30 knots(in the PersianGulf. They decrease •from 75—76°F gusts) during sustained Shamal conditions; on (24°C)inDecemberto73°F(22°C)in January, but increase to 74°F (23°C)in March.

22 THE GULF OF OMAN AND ADJACENT LAND AREAS--M)RTHEAST MONSOON

MESOSCALE SYNOPTIC FEATURES. Low pressure waves imediately southeast oftheStrait of Hormuz may formintheGulfof Oman on slow—moving result in weak east—northeast to northeast frontsthatareorientednortheast—southwest. circulation. Addedtothisisthe effect of a Extensivelow cloudinesswith rain or drizzle terrain—induced low—level cyclonic eddy east of occurs on the east side of these waves. Under theStraitofI1ormuz, Winds near coastlines "Shamal" conditions, the Strait of Hormuz acts show a pronounced land—sea breeze effect because as a venturi; winds increase markedly to the ofmarkedlyhigherterrain and temperatures innediatesouth and southeastoftheStrit inland, Although mean surface winds (as shown proper. Oncea "Persian Gulf Trough" has moved inclimaticsummaries) arenortheasterlyand south off the Iranian coast,a bow—shaped cloud relativelylight,nighttime landbreezesare line—-with the apex of the bow pointing toward southwesterly to west-southwesterly (downslope) the Strait of Hormuz—-forms in the middle of the at 4 to 8 knots. Theseabreeze establishes Gulf of Oman,This cloud line marks convergence shortly after 0900L andpersists through 1900L betweenthewest-northwesterlywinds flowing as north—easterly to easterly onshore flow that over the Omanipeninsulaand the northerly to reaëhes iS to 20 knots in late afternoon, northeasterlywinds flowingofftheIranian coast, The cloud line's dissipation marks the Ahead of an approaching Persian Gulf cold front end of a "Shamal° episode winds turn southeasterly, increasing to 15 to 25 knots. With cold frontal passage, winds veer to become northwesterly at20to30 knots. As the TYPICAL WEATHER. The followingweather is typical "Shamal'builds,windsincreaseto 25 to 40 of theStrait of Hormuz anditsshores during knots, Speeds decreasing to less than 25 knots the Northeast Monsoon: signal the ending of a 'Shamal,' general Sensible Weather. Only high clouds—-often Thunderstorms, Isolatedthunderstormsform over jet streamassociated—-arenormallyobserved theGulf of Oman andalongtheIranian coast here during the Northeast Monsoon.Visibilities inmediatelyaheadofanuppertroughand its remain excellent, except along the Iranian shore associatedsurfacecoldfront, Thestrongest near dawn, when visibilities often fall into the thunderstorms are found over the Omani mountains 3to S mile range, probably caused by very light withcoldfrontalpassage, Topsrangefrom wind conditions thatallow the moistsea air, 40.000 to 50,000 feet (12.2 to 15.2km). advectedinland bythepriorafternoon'ssea breeze,tocondense. Morninglandbreezes, Precipitation. Normal precipitationforthe reinforced by heating and the synoptic northerly season is between 3 and 5 inches (75 to l2Snn), flow, dissipate the haze and fog. but isolated thundershowers may bring much more. Jask, on the Iranian shore, has reported Sky Cover.Extensive middle and high cloud layers 5.6inches(l4Onmi) inJanuary; Jiwani,Paki- occur only inadvance of upper troughs and the stan,8.7inches(220mm). SeebInternational occasionalsurface low that moves eastwardinto Airport, on the Omani coastabout 25 miles Pakistan andIndia. Ceilings range from 7,000 northwest of Ras al'Hadd, has also reported 5.6 to8,000feet(2,100to2.40Dm). Low cloud inches (140mm)in January. ceilings of 1,000 to 1,500 feet(300to450m) are normally confined to the Iranian shore ahead Air Temperatures.Maximum temperatures in January of developing low pressure waves on slow—moving range from 70°F (21°C)to 80°F (26°C) along the coldfronts. Patchylow cloudceilingsform Iraniancoast. Open watertemperatures reach over the Gulf of Oman andthe Omani coast, but 70—75°F (21—23°C). Omanicoastaltemperatures clear within 6 to 12 hours after the surface low average 75°F (23°C). Minimums range from 45 to moves eastward. Middle clouds break with the 55°F (7 to 13°C) depending on exposure. passage of the upper trough. Dust, Widespread dust that restricts visibility SEA SURFACE CONDITIOIG, Gulf of than. is confined to the coasts and imediate offshore Gulfareasduring a strong"Shanal." Dust Water currents are easterly at 0.4 to 0.6 knots in raised by northerly winds on the back side of a January,butbylateFebruary ananticyclonic "PersianGulfTrough'following a Shamal have gyre establishes itself near 2D°N 65°E;current been observedinsatellite imagery,Visibility flow west of 65°E ranges from easterly at 15°N drops as low as3 to 5 miles.Worst conditions tosouth-southwesterlyat20°Ntowesterly at arefoundatthemouth of rivers orcanyons. 24°N, Speeds average 0,5 knots. Wave heights Dustsettles rapidly once winds drop below 25 increase to 2to 4feet during normal northeast knots, Protectedlocations, such as Seeb monsoon conditions. Average wind speeds International Airport on the Omani coast, rarely increase from less than 6 knots just east of the experience visibility restrictions duetodust Strait of Hormuz to10—11 knots as the Arabian during the Northeast Monsoon. Sea is reached.

Winds. WindsovertheentireGulfareaare Watertemperaturesdecreasefrom79°F(25°C)in normallylightandnortheasterly, reflectingthe Decemberto73°F(21°C)inFebruary,thenrise monsoonal flow.Synopticscale gradients to75°F(23°C)inMarch,

23 TIE (WANI AIM8IAN SEA COiIST--AVJRTHEAST MONSOON

NESOSCALE SYNOPTICFEATURES. Noneaffectthe during January. An occasionalthunderstormIS Oniani Arabian Sea Coast. also found among the very isolated showers that occur when stronger onshore winds reach the OCZ. TYPICAL WEATHER. The following weather conditions aretobe expectedinthe DmaniArabianSea Precipitation. Precipitation. along the Irmiediate Coast during the Northeast Monsoon: coast ranges from 1 to 2 inches(25 to SOn). As with therestof thePersian Gulf region, General Sensible Weather.In the absence of upper precipitationisextremelyvariablefromone troughs or fronts, only high clouds associated year to the next, but occasional thundershowers withthe sub—tropicaljet streamare found toward the end of winter have producedi2 to4 here.Visibilities are unlimited. inches(50to100mm). There are few weather reportingstationsin Oman above 1,400feet Sky Cover. Isolatedheavy cumulus occurs when (425m) MSL inland to the main mountain range and stronger onshore winds reach the Omani datais extremely scarce, However, research by Convergence Zone (OCZ)—-see Figure 16. British meteorologists using oil company records Extensivemiddle and highclouddecks also indicates that a total of 0.8 inches (2Onmi) may spread over the region ahead and during passage occur on 4 or 5 days during the season. The of upper troughs Towering cumulus or Hajar Mountains receive up to 4inches (100mm), thunderstorms occur overhigher mountains with mostfrom thunderstormsalongand just behind the passage of cold fronts or upper troughs. coldfronts during January. Icingand turbulence are primarily associated with the Dust. BlowingdustfrolSaudiArabiaatthe cumuliform buildups. heightof a Shamalposestheonly visibility restriction. Dust has been observed well Air Temperatures. Maximum temperatures at offshore both by satellite imagery and by elevations below 1,400 feet (425m) average 75 to embarked US Navy aerologists. Visibilities may 90°F (23 to 32°C).But they decrease with alti- briefly fall to 3 to 4 miles. tude, ranging from 40 to 45°F (4 to 7°C)in the highest mountains, Minimumtemperatures along Winds. Synoptic scale winds east of the OCZ are theiranediatecoast average50 to 55°F(10to northeasterly at 3 to5 knots;west of the OCZ, 13°C); athigher elevations inland, minimums northwesterlyat 5 to 8 knots. Theselarge drop to as low as 20 to 25°F (-7 to —4°C) on the scale patterns, however, are distorted and often highest peaks. overridden by mountain—valley breezes and, along the coast, by land—sea breezes,Winds offshore are predominently northeasterly at 5 to 10 knots SEA SURFACE CONDITIONS, Itthwestern Arabian Sea. along the coast; further out they increase to 10 to 15 knots. Water currents averagesoutheasterly at 3 to 5 knots. Wave heights increase from 3 to6 feet Thunderstormsoccurthroughouttheseasonwith near the coast to5to 10 feet beyond 50 miles eithersurface coldfrontalpassages orupper offshore. troughs. Basesaverage4,000to5,000feet (1,200 to 1,500m); tops can reach as high as Water temperaturescool from 77°F (24°C) in 50,000 feet(15.2 km) withtheraresevere December to 75°F (23°C) inJanuary; with storm. Most thunderstorms occurinthe Hajar increasing solar radiation, they climb backto Mountains along and just behind cold fronts 77°F (24°C) in March,

24 C4apter S

THE SPQIHG TRANSITIOH

(April——May)

144.7CR CLIMATICCOEROLS

FLOW PATTERN REVERSAL. The Spring Transition sees Arabia, and centralIran, NortheastMonsoon thereversalofsynopticscaleflow patterns; pressure gradients weaken early in the completion of this reversal marks the end of the transition. By themiddleofMay,however, Spring Transition and the start of the Southwest strengthening gradients associated with Monsoon, The actualonsetoftheSouthwest extensive thermal low—pressure areas effectively Monsoon isapparentlytriggered by a mid— blocktheeffectsoftheweakeningSiberian troposphericcycloneovereitherthenorthern Anticyclone and restrict cold air outbreaksto Arabian Sea (see "Onset Vortex")or the Bay of early April. Bengal. Incomingsolarradiationincreases dramatically. Changesincirculation occur at THE UPPER—LEVEL (ABOVE 300MB) SUBTROPICAL RIDGE. low levelsfirst. The Northeast Monsoon This ridge, which was oriented east—west between circulation graduallyloosensitsgrip onthe 5 and 1O"N during the Northeast Monsoon, region aslow—levelanticyclonic flow over tie strengthens and moves northward. This movement Arabian Sea isreplaced bycycloniccircu- isdirectly relatedtothe northwardshift of lation. Although the complete transition the Monsoon Trough/Intertropical Convergence averages 30 to 45 days,actual onsets and Zone (ITCZ) and rising upper—level pressure endingsvaryby station location andfrom one above the shallow continental thermal lows, By year to the next.The change can be rapid, The the end of the Spring Transition, the ridgeis end ofthetransitionseason issignaledby anchored by the upper—level high over Tibet. southerly cross—equatorial flow from the SouthernHemisphere moving northward along the INTERACTION BETWEEN TNE POLAR AND SUBTROPICAL JETS east coastofAfrica, then turningsouth- is greatly reduced,As the mean position of the westerly, and finally reaching the Indian PolarJetmoves northward,winter short—wave coast. Once thismoistsouthwesterlyflow upper—air troughs all but disappear. Occasional reacheswesternIndia, numerouspre—monsooral strong upper—level northwesterly winds are thunderstormsoccurovernorthern andwestern possible early in the period. Weak upper—level India. Latent heat of condensation from these flow patterns are common overtheArabian Sea thunderstorms, combined with the increasing duringthetransition. The SubtropicalRidge effectiveness of Tibet as a high—level (SOOoib) separates the easterly flow aloft south of 15"N heatsource,builds a high—levelanticyclone from the westerly flow between 15 and 35°N. As overtheHimalayasandTibet, The resultis theridgemovesnorthward,strongupper—level that high—level westerlies are replaced by high— easterlyflow becomes established over the level easterlieg essential to the maintenance of entire region. the Southwest Monsoon. MEAN MAY FLOW at 850, 700, 500, 300 mb, and 200mb STRENGTHENING CONTINENTAL LOW PRESSURE CENTERS, (5,000, 10,000, 18,000, 30,000 and 40,000 feet) These centers are connected by a thermal trough is shown in Figures 17, 18, 19, 20, and 21. that builds through northeast Africa, Saudi

25 25°E 40°E 60°f 80°f

30°N

20°N

100 N

FIgure 11. Mean May 850mb flow.

250 E

30°N

20° N

100 N

Figure 18. Mean May 100mb Flow.

26 800 E

30 °N

20 °N

10 °N

Figure 19. Mean May 500mb Flow.

80 °E

300 N

20°N

1O°N

Figure 20. Mean May 300mb flow.

27 800£

30'N

20 °N

10°N

Figure 21.Mean May 200mb Flow.

28 TRANSITORY SYNOPTICFEATURES--SPRINGTRANSITION

TROPICAL CYCLONE FREQUENCY ishighestduring TROPICAL STORMS. The meteorological satellite has transition seasons, for these reasons: provided for more accurate location and tracking of Arabian Sea storms;reported frequencies are • Weak cross-equatorialflowintothe Southern naturallyhighersincetheearly1970s,but Hemisphere provides upper-level divergence storms in thisarea are stillrelatively favorable for cyclonedevel opment, infrequent. Between 1890 and 1950, only 14 were r&cordedintheArabianSea during April and • Vertical shear is weak May. Between 1891 and 1969, only eight storms reached the OmaniCoast; favored landfallwas • Low—levelconvergenceincreases duetorapii near Salalah. Stormsusuallyforminthe strengthening of thelow—levelthermal'heat easternArabian Sea between10 and 1514,and lows" in Pakistan,Afghanistan, Iran, and between 70 and 75°E. The strongest have Saudi Arabia. extensivelayeredclouds,lowceilings,heavy rain,andhigh winds outto300 miles of the • The Monsoon Trough/ITCZ migrates northward to center. Flash floods are common. Mean locations between 15 and 2511. April/May storm tracks are shown in Figure 22.

Figure 22. Mean Tropical Storm Tracks--Ajril and May Combined.

29 TIE ONSET VORTEX. The tropical"onset' vortex, LANO—SEA BREEZES become the dominant feature along resembling a tropicalstor'm, occurs only at the coastlines during "undisturbed' (normal)condi- end of the Spring Transition and marks the start tions, Sea breezes are considerably stronger ofthe Southwest Monsoon (hence thename), thanlandbreezesbecauseofstrongdaytime Statistically, it occurs about about 1 year in 2 temperaturegradients. The land—seabreeze inthe Arabian Sea. In other years, a similar effect can cause abrupt changes in temperature, vortex formsinthe Bay of Bengal. Occurrence relative humidity, and wind direction. ranges from mid—May to mid-June and is apparentlythe"trigger"forthedeeplower— level southwesterly flow that marks the Southwest Monsoon, These cyclonic systems form at mid—troposphericlevels overthe surface Monsoon Trough (ITCZ) just •north of the nose of theSouthwest Monsoon current, Movement is generally westwardtoward theOmani Peninsula, southeastern Saudi Arabia,or the Gulfof Oman, Initial movement, however,is northward to about 20°P1, then westward or west— southwestward into the Arabian Peninsula, Layered clouds formover theentireregion within 300mileseithersideofthetrack. There are heavy cumuliform buildups and rainshowerswithin 50 milesofthecenter, Convective clouds and precipitation are greatly intensified overthe OmaniMountains even when the vortex does not actually reach them,

THE ISERT FRONT. Actually a mean polar frontal positionoverthenorthern RedSea,the desert front is not active every year,It does, however, represent a relatively rare storm track that lies acrosssouthernEgyptandthenorthern Red Sea into central Saudi Arabia.This storm track often Figure 23.Mean Position of the Desert Front. results in the formation of a secondary wave over thecentral Red Sea as the mean jet stream position is displaced southward over the southern Mediterranean or northernAfrica. Extensive thunderstorms and heavy rains accompany the movementofthesecondary low acrosstheSaudi Arabian peninsula, This track is only present In late winter (March) and during the spring transition. In May 1972,Riyadh,SaudiArabia, twiceexperienced passage of a desertfront, Although variationsintemperatureandwind may 25! help identify the surface frontal position, there are times when this disturbance loses its surface characteristics; when itdoes,theonlyindi- cations areinits associated weather and upper- leveltrough, Thesefast-movingfronts/troughs canaffect a station'sweather for2-3hours; they are often restricted to the area west of the Strait ofIlormuz. Mean position of the desert 20N front is shown in Figure 23.

TIE ONANI CONVERGENCE ZONE (DC!), The OCZ marks the boundary at which the predominant low—level northwesterly flow meets the intensifying southwesterly flow ahead of the Southwest Monsoon. Although the OCZ is mainly delineated by wind shear across it, occasional convective •1 activity can be found over higher terrain. By the end of theSpring Transition,the Monsoon Trough/ITCZ has moved into the OCZ. Figure 24 gives the mean April location of the OCZ. Figure 24.Mean 'il Position of the XZ.

30 TIlE PERSIANGULF PROPER AND ALUACENT LAND AREAS--SPRING TRANSITION

HESOSCALE SYNOPTIC FEATURES, As the Spring withseverethunderstorms. When strong winds Transitionprogresses, the Omani Convergence are not sustained, dust settles rapidly. lone(OCZ) moves northwestward into the extreme southern Persian Gulf. This movement is due to Thunderstor.s, Tops often exceed 40,000feet the strengthening thermal lows over Saudi Arabia (12.2km); basesaveragebetween4,000and combined with increasing southwesterly flow over 6,000 feet (1,200 and 1,800 meters.) The usual southeastern Arabia and the Arabian Sea. severeIcing and turbulencecan beexpected, Hailshould be assumed when the classic Killer TYPICAL WEATHER. The following weather conditions AWSTR-200 wetbulbzeroheights above terrain are typicalofthe Persian Gulf proper during are met. Thunderstormsduringthe Spring the Spring Transition: Transition have several causes:

General Sensible Weather. Cloud coveris nearly • Fronts. AnoccasionalMediterranean frontal nonexistent save for the rare thunderstorm. The system reaches the region early inthe trans- few instances of jet stream cirrusare almost itionseason, Althoughconsiderably weaker totallyrestricted to upper—level westerlies thanfrontsthatoccur duringtheNortheast early in the period.Fog can occasionally occur Monsoon, these can be strong.enough to trigger early in the period, but only in early morning. thunderstorms. Floodingin the Tigris—Euphrates River Plainis coninon, and caused bymelting snowfromthe • Intense heating over coastlines allows mountains of Iran and Iraq. Flooding has become convection to penetrate low—level inversions. more of a problem ince 1980 when flood control levees were destroyed during the Iraq—Iran war. •Strong sea breezes lift moist air orographically over nearby coastal mountain ranges. Sky Cover.Middle and high cloud decks occur only with those few upper—air troughs that penetrate S Mid—level unstableairassociatedwith an theareaearlyintheTransition, Ceilings upper—level trough (or with a weak Mediterra- rangefrom 10,000to14,000feet(3.1to4.3 nean front)is lifted orographically over the km). Lower ceilings are associated with Zagros mountains. thunderstorms, which see, Lighticing and turbulence occurin middle cloud decks near the Late in the transition, but veryrarely, trough axis, thunderstorms may also form over mountains along and southeast of the OCZ, Winds. Weak low—level winds reflect the macroscale pattern reversal, Late in the Precipitation.Rainfall decreases steadily during period,windpeedsIncreasetoreflectthe the transition, Its convective nature results development of strong continental thermal in high variability from one location to another lows, April speeds average 5-7 knots, andfrom one yeartoanother, Mean values of increasingto10—12 knotsinMay. Directions 0.50to1.0P inches(13to 2Gm) earlyin the continueto be northwesterlyinthenorthern transition decreaseto less than 0.50 inch Persian Gulf, westerly in the southern Gulf, and (13mm) by early May, thentonear zero by the turning southerly as one approaches the Strait start of the Southwest Monsoon, Much more may of Hormuz, On the imediate coast, winds show fall over the Zagros during isolated large diurnal changes due to land-sea breezes,, thunderstorms; flash floods have occurred. Dust and Sand. The most significant weatheris Air Temperatures.Temperatures rise significantly theincreasingfrequency ofblowingdust and duringthe Spring Transition, Daytime maximums sand. Late season frontal zones (desert fronts) in coastal regions climb to between 95 and 97°F can advect dustor sand acrosstheentire (35and 36°C). Mean May temperatures onthe northern part of the Arabian Peninsula, Latein north shore of the Persian Gulf are even higher; the Spring Transition, strengtheningnorth- for example, 101°F(38°C)at Abadan,Iran, and westerly windscauselowervisibilities,with 102°F (39°C)at Kuwait. Inland temperatures in highest frequencies inthe northern part of the Saudi Arabiastaywithin a fewdegreesof Persian Gulf. Visibilities drop to less than 6 coastaltemperatures, Zagros Mountain tempera- miles duringthe day; inthe afternoon, with tures are nearly 5°F (2.8°C) cooler than coastal higherwindspeeds,visibilities droptoless regions. Minimum Apriltemperaturesatmost than 3 miles,Basrah, Iraq, and Kuwait, Kuwait, locations rangefroe 62to &5°F(16to19°C). both average nearly 10 days a month with blowing warming rapidly to 73 to75°F(22to 23°C)in sand or dust.Blowing dust or sand also occurs May. Iranian mountain locations are nearly 10°F with the rare thunderstorm——most of which occur (5°C) coolerinbothmonths. Dewpointsin early in the Transition, Visibilities in coastalregions rangefrom50to53°F(10to stronger thunderstorms may drop to aslow as a 11°C). Dewpoints drop dramatically inland, half mile;near—zero visibilities are possible

31 SEA SURFACE CONDITIONS.PersianGulf.

Water currentsin the PersianGulfcirculate Water temperatures rise rapidly during the Spring counterclockwise. A steadyflowofsurface Transition. Surfacewatertemperatures range water enters the Persian Gulf through the Strait from 73 to 76°F (22 to 23°C)in April to 80—82°F of Hormuz. The surface current flows toward the (26—27°) in May. TemperaturesInextremely west,thennorthwestas ithugstheIran Ian shallow coastal. waters may get 5 to 7°F (2.8°to shore. Atthenorthern endof theGulf.it 3.8°C) warmer.With the warming surface waters, turnssoutheasterlytoparalleltheArabian theretendsto be an increasingtemperature coast. Finally,itturns northerly along the difference betweenthesurfaceandthe bottom west side of the OmaniPeninsula to join fresh (about 195 feet or 60m);by May the bottom is Gulf of Oman water entering through the Strait about 10°F (5.6°C) cooler,There Is no evidence of Hormuz, Speedis less than 1 knot. Maximum of thermoclines.Wave heights are less than 4 calculated speed for the 100—year worst case of feet (1.2m) more than 80% of the time. bothwindand tidalcurrentswas 8 knots at Jubail, As waterincreasesindensity,it sinks, turns southeastward, and flows back into the Gulf of Oman as a bottom current through the Strait of Hormuz.

32 TIE STRAIT OF 1101 WIUZ--SFQING TRANSITION

MESOSCALE SYNOPTIC FEATURES. None apply Dust is confined to rare cases of advection from specifically to the Strait of Hormuz. thenorthernPersianGulforcentral Saudi Arabia following frontal passages,Visibilities normally remain above 6 miles, but visibilities TYPICAL WEATHER. The following weather conditions aslow as 3 miles arepossibleif thesource are typical of the Strait of Hormuz during the regioniscentralSaudiArabia, Lowervisi— Spring Transition: bilities are possible only with an active desert front, GeneralSensible Weather. Cloud cover decreases fromnear 3 eighthsinAprilto 1 eighthin Th.mderstorms. Although rare, thunderstorms can May. Thisisthe only season of the yearin occur over the mountains on either side of the which theusuallate evening and early morning Strait. Stormsarestronger overtheZagros patchy low stratus and stratocumul us are mountains. Causes and characteristics are much absent,Visibilities are excellent, the same as forthose inthePersianGulf proper, which see. Sky Cover. Middle and high clouds are found only with the infrequentlate winter frontor Precipitation occurs only with the rare trough. Ceilings average 12,000 to 14,000 feet thunderstorm and isconfined tomountainous (3.7 to 4.3 km).Light mixed icing and light to areas without reporting stations, No moderate turbulence——especially over the Zagros measurements are available, but crude estimates mountains ontheIranianshore——are associated derived from similar situations in Arizona give with these layers, Convective clouds may form values of 0.25 to 0.75 inches (6 to l9nvn). in late afternoon, especially along the Straits Iranianshore. These clouds are caused bya AirTemperatures. Maximum temperatures average combination of strong land-sea breeze from 97to99°F(36to37°C). Minimums rise interactionand mechanicalliftingover nearby from the lower 70s (about 22°C)on the Iranian higher terrain.They have relatively high bases shore in Apriltothe upper 70s (about 24°C) by at 5,000 to 7,000 feet (1,500 to 2,100 m). May, On theArabianshore,temperaturesare slightly lower, warming from the upper SOs (near Winds. General flowissouthwesterlytowest— 20°C) inApriltothelowlOs (near22°C)in northwesterly west of the Strait and northerly May, Temperatures farther inland are cooler due to northeasterly east of the Strait. Low—level toincreased elevation and the diminishing sea flow reflects a combination of the weak inflow breeze effect, from theGulfof Oman, pronounced land—sea breezes(especiallyalongtheIranianshore), and a generaleasterlytosoutheasterlyflow SEA SURFACE CONDITIOI'6, Strait of Hormuz. aroundthe southern endof the terrain—induced leeside Gulf low,Bandar Abbass (on the Iranian Water currents through the Strait are mainly tidal shore)maintains the mean southerly flow found ebb and flood, During ebb conditions, currents inthe otherseasonswhileDubai,United Arab of less thanIknot flow predominantly from the Emirates, finds its mean wind direction changing Persian Gulf through the Strait into the Gulf of fromwesterlytosoutherly. Theabsenceof Oman. Floodtide currents(alsoless than 1 disturbancesleavestheflowpatternofthe knot)reverse to flow from the Gulf of Oman into southern shore ofthe Strait tothelocal the Persian Gulf.Waves heights are less than 4 patterns of the leeside low and land—sea breeze feet (1.2m). circulation,Complicating these patterns is the pronounced venturi effect through the narrowest Water temperatures warm from near 77°F (24°C)in part of the Strait, Sea breezes strengthenin April to 82-83°F (27—28°C)in May. May as thermal lows build over the continents.

33 THE OJLFOF (flN AND ALUACENT LAND AREAS--SEWING TRANSITION

NESOSCALE SYNOPTICFEATURES. Iranian shore turn east—northeasterly and increaseinspeed during daylight hours as one Tropical Cyclones. Tropical cyclones that approaches the Strait of Hormuz.This is due to originate in the Arabian Seaonlyreach the Gulf the strengthening sea breeze influence as well Of Oman about once every 4 years, They produce as the Omani Gulf Low described earlier. Toward layered clouds,low ceilings, heavy rains, and the end of the season weak southwesterly flow, highwinds. Intherarecases of landfall. often masked by local effects, appears along the expectflashfloodsinand near mountainson Omani coast.Speeds average 3 to 5 knots, either coast. Moderateicingand moderate to severe turbulence are common, but turbulence and list is almost unknown.Blowing dust or sand may icingare heavier over the mountains on either occurwiththerarethunderstormoverhigher shore.Ceilings can be as low as 1,000 to 1,500 mountains on either side of the Gulf Of Oman. feet(300to 45Dm)withlayers through 40,000 feet (12,2km). Visibilities can be as low as Thunderstorms, A very rare thunderstorm may occur •half a mile, and windscan beofhurricane overhigher mountains on both theIranian and force. Thereareno records of maximum wind Omani shores of the Gulf. The most common cause speeds; not many of these stormspassed over is locally induced convection resulting from the reporting stations, and those that did destroyed lifting of moistGulf air over nearby coastal the anemometers. Although more than 10inches mountain ranges. Although infrequent, the most (250mm)of rain were recordedina storm that conmion locationis in Oman's Jabal Akhdar made landfallnear a reportingstation,there range, Thunderstormtopsoftenexceed40,000 have undoubtedly been higher amounts. feet (12,2 km); bases average between 4,000 and 6,000 feet (1,200 and 1,800 meters.) The usual Omani Gulf Low, This mesoscale low is locatedin severe icing and turbulence should be the western Gulf of Oman; it dominates during expected. Hail should be assumed when the the early part of the transition season.It is classic Miller AWSTR-200 wet bulbzero heights caused by a combination of a Zagros Mountain lee above terrain are met. side effectandthe mountainous terrainalong the Omani coast, As theNortheast Monsoon Precipitation. Exceptforthatfromtherare weakens, so does the low. Establishment of the tropical cyclone, precipitation is thunderstorm— Southwest Monsoon destroys this mesoscale associated,almost alwaysfallingin mountains feature,.See 'Winds.' where there areno reportingstations. Crude estimates based on similar situations in Arizona indicate amounts to be 0.25 to 0.75 inches (6 to TYPICAL WEATHER. l9nm.

GeneralSensibleWeather, Thisisperhapsthe Airtemperaturesincreaserapidly due tothe mostsettledseason of the yearinand around combination of decreased cloud cover and theGulfof Oman, Skiesarenormally clear undisturbed (normal)weather conditions. Max- with excel lentvisibil ities. Mid—latitude imum temperatures on both shores of the Gulf of disturbances from the Mediterranean rarely have Oman warm from between 87° and 89°F (30 to 31°C) the support toreach this farsouth, The OCZ inAprilto between 94 and 96°F (34 to 35°C)in moves intotheextremesouthernPersianGulf; May, Minimum temperatures on the southern coast the Monsoon Trough/ITCZ has yet to appear. risefromnear80°F(26°C)inAprilto85°F (29°C)in May. Maximum temperatureson the Sky Cover. Latein the Transition season, cirrus northern coast are nearly 5°F (2.8°C) cooler. layersare sometimes advected westward from tropicaldisturbances intheeasternArabian Sea. These layers reach the area only when the SEA SURFACE CONDITIONS. Gulf of Oman, upper—level easterlies have setup south of the subtropicalridge. The cirrus dissipates near Water currentsbecome southwesterly,averaging the eastern portion of the Gulf of Oman due to only half a knot throughout the Gulf of Oman and strong mid—tropospheric subsidence, northernArabianSea. Wave heightsareless than 4 feet (1.2m) nearly 90% of the time, Winds. Thelight and shifting synoptic gradient duringthefirstpartofthisseasonleaves Water temperatures rangefrom 78°to79°F (near winds over land atthe mercy of localeffects 25°C) inAprilto83to85°F(near29°C) in such as land—sea breezes and/or mountain—valley May. breezes. Low-level winds along the innediate

34 OMAN! ARABIAN SEA COAST--SPRING TRANSITION

NESOSCAIE SYNOPTIC FEATURES. Nasirah become southwesterly by May. Winds at Salalah movefromthesoutheasttosouthwest, Tropicalcyclones originatinginthe ArabianSea Wind speeds are neartheir annual minimum. may affect the Omani Coast, but incidence is not Earlymorninglightwindsincrease throughout high. On the average, one of these storms may theday to7—9 knots by mid-afternoon. Winds make landfall on the Omani coast in only 1year over the northwest Arabian Sea become out of4. For characteristic conditions, see southwesterlybymid-Aprilat 4 to 7 knots. 'MesoscaleSynopticFeatures'fortheGulf of Directionsstayconstant through May, with Oman and Adjacent Coasts. speeds increasing to 10 to15 knots just before the onset of the Southwest Monsoon. Onset Vortex. The onset vortices that mark the end of this transition season andthe start of Thunderstorms. Although none have actually been the Southwest Monsoon (see 'Transitory Synoptic recorded here, they probably do occur. British Features") reachthe Omani Arabian Seacoast meteorologists working with oilexploration lessthan 25 percentofthetime. Layered companiesintheinteriorhave observedrare clouds occurfrom 1,000 to3,000 feet (300 to cumulonimbusoverthe mountainstothe south- 1.000m) upto35,000to40,000feet(10.7tb west, 12.2km)overthe entire region within 300NM of the vortex center. There are heavy cumuliform Precipitation occursonlywithtropicalstorms, buildups and rainshowers within 50 miles of the thunderstorms, orthe passageof an onset center, and moderate icing and turbulence within vortex. Amounts inexcess of 10inches(255nn) 150 miles of the center. Flash floods inand have been recorded, near theOmani mountains are commoneven when the vortex does not actually make landfall. Temperature, Thisisthe warmestseason of the year. Maximum and minimum temperatures are at their highest annual mean at both Salalah and TYPICAL WEATHER. Masirah. Maximums average from 90 to 96°F (32 to35°C); minimums from 77 to 78°F (near GeneralSensible Weatherisexcellent. Thisis 24°C) themostcloud-freeseasonoftheyearhere; visibilities are excellent. SEA SURFACE CONDITIONS, Northwest Arabian Sea. Sky Cover. Multilayered cloud decks are confined to those associated with the very rare tropical Water currents begintoestablish themselves as cyclone (see "Mesoscale. Synoptic Features"). southwesterly at 1 to2 knots by the end of the season. Dust.As wind speeds rise late in the season with increasingsouthwesterlyflow, and theground Water temperatures climb totheir highest values becomes baked by high temperatures, the number of theyear, reaching between 79 and 81°F (26 of days a month withblowingdustor sand and 27°C) . The fact that water temperatures are increases. Byseason'send,blowing dustor at their warmest now, rather than laterinthe blowing sand occurs on 4 or 5 days a month, surmeer,isa result of the low cloud cover and extensiveupwelling thatestablishes almost Winds. Winds switch to southwesterly in late May coincidentally with the onset of the Southwest or early June to herald the end of the Monsoon, Transition Season,Northeasterly winds at

35 Chapter 6

THE SOUTHWEST MONSOON (.June--SeptSier)

MAJOR CLIMATIC CONTROLS

A MASSIVE ThERMAL LOW—PRESSURE TROUGH dominates the Straitof Hormuz, Aftercrossingthe this season. This trough has its primary axis Strait of Hormut it lies at or near the 1,640 along the Persian Gulf, with a secondary center foot (SOOm) contour lineof the Zagros over southcentral Saudi Arabia, Itis a Mountains--or about 25 to 30 miles inland of the westwardextensionofthe summerthermallow Iraniancoast, Upon reachingextremewestern centeredin extreme westernPakistan, The PakistannearJiwani,theMonsoon Trough/ITCZ entire systemisanchoredby a combination of turnsnorth—northeastward. Unlikeinother terrain (the Zagros mountains along the Iranian tropicalregions, the Monsoon Trough/ITCZ here PersianGulf shore)andthe extremely hot and marks the boundary between moist tropical air at dry air over the Arabian Peninsula, low levels and hot, subsiding air above,It is, therefore, normally inactive.It slopes gradu- AN UPPER—AIR RIDGEhas. formedovertheArabian ally upward towards thesoutheast,andis the peninsula and Iran, 500mb high pressure centers cause of the extremely strong elevated inversion are located over extreme western Arabia and over southandeast ofItssurfaceposition. In the Zagros mountains in southwestern Iran. southeastern Saudi Arabia and Oman, the Monsoon Trough/ITCZabsorbs the OmaniConvergence Zone THE NONSOON TROUGH/INTERTROPICAL CONVERGENCE ZONE found duringtheNortheast Monsoon and the (ITCZ) enters the study area about 200NM Inland Spring Transition, Figure25showsthe mean of Salalah on the southwestern DreaM Arabian Sea July surface position of the Monsoon coast and follows the Omani mountain crest to Trough/ITCZ,

Figure 25.Hem, July Surface Fositi3n of the ?bnsoonTrough/lTd.

36 Figure 26 is a mean July1200Zsoundingfor the high—speed winds of the Southwest Honsoon, Salalah, on the Arabian Sea Omani coast. It also results in a stratocumulus deck offshore Although the soundingis based on limited data, thatturnsonshoreinthelee of peninsulas, theinversionprofileshownis believedtobe This deck behaves likeCalifornia coastal representativeof the southeastern Arabian stratus. Peninsula andinnnediately offshore that liein the 'Southwest Monsoon,' discussed next, THE TROPICAIEASTERLY JET(TEJ), Thenorthern edgeofthe TEJ crossesthe southem Arabian Peninsulaand the northernArabianSea from east to west, Maximum speeds(in thearea of this study)are50 to 75 knotsbetween40 and 45,000 feet (12.1and 13,6km),

TWO IMPORTANT AIRFLOW FEATURES. • A northwesterly current at alllevels over the Arabian Peninsula, Extremely dry, this flow is the primary atmospheric cause for the prevailing dust layer found throughout the region, Embeddedinthis currentistheSunner Shamal that occurs over and just west of the Persian Gulf, This enhancement ofthe prevailing northwesterly and northerlyflowisnormally strongest during June and July. • Hid—level easterly to southeasterly flow at 700 through 500mb over Iran and at 600 through 500mb overthe OmaniPeninsula. Itoriginates with the mid— and high—level anticyclonecentered over Central Iran and western Pakistan,

Mb—LEVEL MOISTUREovertheIranicoastofthe Gulf of Oman, the Zagros Mountains and westward overthe Omani Peninsula. Duringperiodsof strongerflow,isolatedthunderstormsdevelop over all three areas.

A PERSISTENT MID-LEVEL TROUGH at600and500mb over the southern portion of the eastern Arabian Figure 26. Mean Winds, Tenqrratures, and Peninsula separates the northwesterly and Geopotentials--Salalah, 12001,July19&0. southerly flows. Experienced British meteorologists think this relatively weak trough is the cause oftheoccasionallythickaltocumulus THE SOUTHWEST MONSOON,for whichthisseasonis layers found here. named,is a deep and strong sustainedflow of southwesterly to westerly winds over the entire EXTREMELY WARM PERSIAN GULF WATERS. The shallow Indian Ocean north of the Equator, Flow depth waters of the Gulf heat rapidly and remain hot overtheCentralArabian Sea and theIndian throughout the suirmier. Surface water Ocean extends from the surface to above 500mb, temperatures by mid—July are above 90°F Thisflow liesonthe equatorward side of the (32°C) . Highevaporationratesresultin a Monsoon Trough/ITCZ. Strongest speeds are over steady northwestward flowofsurfacewater easternAfrica and immediatelyoffshoreof through the Strait of Hormuz into the Gulf; the Arabia,The core current of this high—speed air current just west of the Strait reaches 2 to 4 isknownas the "SomaliJet,° Normal maximum knots, A counter—currentflowssoutheastward depth of the moist tropical airin this airflow along the bottom down the Persian Gulf and out along the Arabian Coast and in the Gulf of Oman intothe Gulf of Oman. Note that the surface is2,000 to 3,000 feet (0.6 to 0.9km).itis current into the Persian Gulf flows against the capped by astrong inversion that rises toward prevailing northwesterly winds, the southeastoverthe Arabian Sea. This inversion marks the Monsoon Trough/ITCZ, MEAN JULY FLOW at 850,700,500,300,and 200mb (S,000, 10,000, 18,000, 30,000, and 40,000 feet) STRONG UPWELLINGalong and justoffthe Omani are shown in Figures 27 through 31. Arabian Sea coast assists in the maintenance of

37 E

30 °N

20 °N

1O°N

Figure 27. Mean July 850mb Flow.

80° E

30 °N

200 N

10°N

Figure 28. Mean July 700mb Flow.

38 800 E

30°N

20 °N

10°N

Figure 29. Mean July 500mb Flow.

300N

200 N

10 °N

Figure 30. Mean July 300mb Flow.

39 80° E

° 30 N

20 °N

10 °N

Figure 31. Mean July 200mb Flow.

40 TMP6ITLWY SYNOPTIC FEATURES--SOUTHWESTMONSOON

WEAK UPPER-LEVELTROUGHSINTHE WESTERLIES. lii Tropicalstormoccurrencedropsoffmarkedly June and early July these troughs may penetrate with the onset of sunner as the monsoon southwardintotheArabianPeninsula when a trough/ITCZ moves northwestward to a lifle blocking high over northern Europe results ina through thesoutheast ArabianPeninsula across high—speedwindcoreinthe westerlies across theStraitofHormuz and eastwardalongthe the Mediterranean into Iraq.The characteristic Iranian Gulf of Oman coast into extreme western middleand highclouds associatedwiththese Pakistan, Elevenstorms were recorded during troughs show up well on visual andBR satellite the month of June between 1890 and 1950. Imagery. Between 1891 and 1969, five made landfall on the Omani coast, Occurrences In Julythrough NORTHWESTWARD MOVEMENT OF THE MONSOON TROUGH! ITCZ Septemberare rare; only sevenwere observed intOthe southernPersianGulf and Arabian overtheArabian Sea between 1890and1950. Peninsula. The Monsoon Trough/ITCZnormally Storms that do form and surv lye the infl uênce of lies over southeastern Arabia and the Strait of colder water foundin the extreme eastern Gulf Horniuz, and alongtheIranianGulfof Oman of Oman and along the northeastern Arabian coast shore,butundercertainconditions,itwill make landfall near Salalah on the central Omani move furthernorthwestwardintothesouthern coast. part of the Persian Gulf. This movement results from pulsesinthe Southwest Monsoon that are One storm is known to have crossed the northern most prevalent inJuly, August. and early Arabian Sea during August; It made landfall at September. Pulse origins are; Maslrah, Winds of 47 knots and atotalstorm rainfall of 1.77 Inches (45.0mm) were Easterly troughs moving westward over the Indian recorded. The surface pressure gradient Ocean inthe southern hemisphere trades. These tightened rapidlyin the southern PersianGulf tradewinds,recurvingtowardtheeastafter at the same time;Abu Dhabai and Dubai recorded crossing theequator, become the"southwest easterly winds gusting to 37 knots with monsoon," Increased mass transport behind the visibility5/16mile(500m) inblowingsand, troughs reinforces the Somali Jet and results in Masirah has recorded much higher storm higher wind speeds. rainfall; for example, 17 inches (43Ormn)fell during the June 1977 storm.Although there are Shear lines moving northeastward up the no observingrecordsfortheOmani mountains, Mozambique Channel between Africa and precipitation amounts are doubtless higher Madagascar. Theseshearlinesoriginate as there. southernhemispherecoldfronts, The ridges following them provide the additional mass that, aftermergingwiththeex-southern hemisphere trade windsovereasternKenyaandTanzania, resultsinincreasedwind speeds of the Somali jet.

THE ONSET VORTEX hasbeenthoroughly discussed under the Spring Transition in Chapter 5. However, readers should remember thatthis feature actually straddlestheend of the Spring Transition and the startofthe Southwest Monsoon. Itisan Arabian Sea tropicalvortex associatedwiththeonsetofthe Southwest Monsoon. It occurs in1 out of 2 years.Either this vortex,or a similar oneintheBay of Bengal ,seemsto be a necessary condition for establishmentofthe upper—level anticyclone over Tibet and the Himalayas.This anticyclone, whichactsas the monsoon outflow,inturnis necessary for formation and maintenance of the upper—leveltropicaleasterlies, Forfurther details, see "Transitory Synoptic Features" under 'The Spring Transition,"

TROPICAL CYCLONIC STORMS/CYCLONES are late spring- early suriner phenomena, almost always the remainsofBay ofBengal cyclonesthatcross Figure 32,Mean TropicalStorm Tracks, June. India,regenerate In the Monsoon Trough—ITCZ over the extreme northern Arabian Sea, and then movetowardthewest. Junestorm tracks are shown In figure 32.

41 THE PERSIANGJLF PROPER AND ADJACENT LAND AREAS--SOUTHWEST IICASOON

MESOSCALE SYNOPTIC FEATURES. The following low causes thetightenedgradientthat is features are common to the Persian Gulf proper and partiallyresponsibleforthelow-leveljet its immediately adjacent land areas: described below.

The Sumier Shamal describes the prevailing The Low—Level Jet, From thecombinationof northwesterly windsthat occurthroughoutthe terrain and synoptic features already described, Southwest Monsoon season but are strongest from a high—speed, low—altitude wind maximum, or earlydunethroughmid-tolateJuly, The "low—leveljet'(LU) ,persists for most of the Summer Shamal winds result from a combination of southwest monsoon season along the Arabian Coast flowaround the Pakistani semipermanentlow from about 75 miles southeast of Kuwait to100 pressure area, theSaudiArabian heat low, the miles southeast ofDoha. The changing terrain "valley'of thePersianGulf,andthe barrier orientation between Doha andAbu Ohabi resuls effect of theZagrosMountains thatinduces a inrelaxation of conditionsfavorablefor LU mesoscale low pressure area over the gulf near formation, Speeds within the LUcan exceed 50 the Iranian shore. knots; altitudes of thestrongest wind speed cores are between 800 and1,500 feet (245 and A Nesoscale Lee—side Induced Surface Low lies over 460m) MSL, As with allLU.Js, altitudes and core the southeastern Persian Gulf, anchored against speeds are subjectto diurnal variations; the the Iranian coast. Caused by complex lowestaltitude of thewind maximum, andthe interactions between terrain features (the highest speeds, occur just before dawn. Figure Zagros and Omani mountains) and the Summer 33 shows a representativecase, In late Shamal winds, thelowresultsinlow—level afternoon, speeds drop to those of the gradient easterly and southeasterlywinds along the wind. Iranian coast as far northwest as Busheir, The

WIND DIRECTION I I I WIND SPEED (KTS)

320 340 360 FEET 300 3000

2000

1000

0 10 20 30 40 50 KTS

Figure 33.Low-Level Wind Profile Over Bahrain.

42 Extremely dry soil. Windsabove 15 knots pick up Dust. The major Southwest Monsoon weather hazard drysoilparticlesto form theever-present throughout the Persian Gulfregionis the suspended dust that isacharacteristic feature suspendeddust and sandraisedbythestrong ofthisregionduring theentire Southwest northwesterly low—levelwindsofthe "Surmuer Monsoon. Windsabove 25 knotspick upthe Shamal." Suspended dustinthe atmosphere here heavier sand particles. restricts visibility to 3to5 miles.The tops of this persistent dust layer are between 13,000 DustDevils, Thesevortexphenomena occur over feet (3.9km) and 16,500 feet (5.1km) MSL. land areas throughout thePersian Gulf region, Visibilityin the dust varies as a function of The strongestoccuralong coastlinesinthe low—levelwindspeed: thestrongerthe wind, vicinity ofsea breeze"fronts.' Duringlate the lower the visibility. Much of the dust has morningand afternoon,risingthermalsinthe beenpicked up fromtheIraqidesertstothe hot air just inland of advancing sea breezes are southwestandwest ofBasrah, Criticalwind reinforced and twisted by the moist, cooler air speedforlifting the dustinto the atmosphere of sea breezes. The resulting dust devils rise isabout15knots—-a conditionthatis nearly to heights of over 330 feet (100 meters), They constantduringJuneandJuly. Thecritical canbe advectedinlandseveral miles along the speedis raised to 20 knots after showers, but sea breeze "front" before dissipating, heavy vehicular traffic lowers it to 10 knots. Extensive damage has been reported. Considerably lower visibilities——sometimes near zero——can occurthroughout the season as a TYPICAL WEATHER. The following weather conditions resultofstrongersustainedwindscausedby may be expectedintheimmediatePersian Gulf shearlinesembedded in thewesterliesthat area during the Southwest Monsoon: penetrateintosouthern Iraqand/or extreme northern Saudi Arabia, Theseconditionsare General Sensible Weather over the Persian Gulf and most common inJune and earlyJulyand are the Arabian Peninsula normally consists of high surfacereflectionsofthe weak upper-level clouds, Patchy low stratus willform along and troughs that produce the rare thunderstorms to justwestoftheArabiancoastfromDhahran be discussedlater, Winds behindthese shear southeastwardinlateevening. Stratusforms lines canexceed 30 knots;peak winds of 35to due toa complex combination of land breeze, sea 45 knots havebeen recorded as farwest as breeze, and summer Shamal strength. The Riyadh andasfarsouthasDubai. Such winds "Terminal Forecast Reference Notebook for generate a"haboob" type wall of dust.Tops of Dhahran, SaudiArabia,"contains an excellent thedustwall havebeen reportedas highas discussion of the subject. Similar conditions 19,000 to20,000feet MSL. Insuchcases, have beennoted by forecasters atDoha,Oubai "clearing"can be saidtohaveoccurredonce and Abu Ohabi. Visibilitiesthroughoutthe winds dropbelow 15 knots and visibility returns region during June and early July average from 3 to the "normal" 3 to 5 miles to 5 milesin suspendeddust. Visibilities after mid—July normally improve to 3 to 7 miles, Sustained occurrences of very low visibility are stillin suspended dust. tiedtotheexistence ofan Omega blockover northern Europe, and the resulting depression of Sky Cover. Upper—air troughs early in the season the westerliestothe latitude of the southern produce patchy layered middle and high clouds in Mediterranean.Bahrain visibility distributions which light icing isfound. Bases average from (shownin Figures 34 and 35)are representative 14,000to16,000feet(4.3 to4.9km). Very of normalconditions alongthe Arabian Persian rarethunderstorms may formalongthetrough Gulf coast. axis;tops may reach 45,000 feet (13.7 km)

Figure 34. Percentage Frequencies of Yisibilities 3If, Bahrain.

43 I-• —

4 I

I A I — — . _L. ' I 0500 0700 0900 lao 1.300 'SOC 100 900 2'OO 2300 t Figure 35.Perca9tage Frequencies of Visibilities S 1100 Yards,Bahrain.

Winds over the northwestern half of the Gulf are an increase in low—level moisture from either of sustained northwesterly at10 to20 knots with severalraresources, Thesesourcesinclude: muchhigher gusts,allreflecting the°Surmiier enhancement ofthe persistenteasterly and Shamal,' A low-leveljet(LU) along the southeasterly mid—levelflowaroundtheupper Arabian Persian Gulf shorefrom about 75 miles air Iranian anticyclone; a Bay of Bengal monsoon southeast of Kuwait to100 miles southeast of depression that maintains itself westwardinto Doha is a common occurrence, The changing the northwestern Arabian Sea; and a terrain orientation between Doha andAbu Ohabi northwestward movement of the Monsoon results in weakening of conditions favorable for Trough/ITCZ, The latter allows southwest LU formation, Wind speeds within the LU can monsoonmoistureto feednorthward(oreven exceed 50 knots; altitudes of thestrongest northwestward)into the Zagros. Intense summer wind speed cores are between 800 and 1,500 feet heatingprovides thenecessary triggerinall (245 and 460m) MSU. Average surface speeds are these cases. 15to 20 knots,Winds in the southeastern half of the Persian Gulf reflect both the circulation Precipitationreachingtheground,exceptfrom aroundthe southern endof the leeside—induced very isolated showers over the Zagros Mountains, mesolow and the west-to—east orientation of the is nil. Even with the rare thunderstorm, much, mountains ontheIranian shore. The south-to— ifnotall,precipitationevaporatesbefore north alignment of the mountains onthe Omani reaching the ground. PeninsulaoftheArabiancoastcombinewith these otherfeaturesto'turn"the prevailing AirTe.perature. Daytime maximum temperatures winds——first westerly, then southwesterly, alongtheirrmiediatecoast average between105 finally southerly——as one approaches the Strait and 111°F(40to 44°C). Inland,temperatures of Hormuz fromthe west, Land andsea breeze riseto 115to120°F(45to50°C), Minimum circulations , of course, modify this pattern, temperatures along the coast fallto 75to 79°F which can only be overcome by a strong (23—26°C). DespitehighPersianGulfwater 'Shamal.' Evenunder these conditions, winds temperatures, dew points along even the over water and along thePersian Gulf coast of irrmied iatenortherncoastl me rangefrom56°F theOmani Peninsulawillback only asfaras (13°C)in June to 66°F (18°C)in September. The westerly. Average speeds over the Iranian side southernArabiancoast hasmarginallyhigher rangefrom10to15knots,or 5 to 15 knots dewpointsbecauseofflow offthe water,but lowerthanon theSaudi Arabianshore. The they drop rapidly as one moves inland. Riyadh higher speeds on the Arabian—Omani side are not averages a 35°F(3°C) dew pointthroughthe surprising; thisistheregionoftighter summer, with correspondingly lower minimum mesoscale gradientin phase with the prevailing temperatures. Beyond20 to30milesinland, macroscale northwesterly flow, minimum temperatures drop to75to 85°F (24 to 29°C) Thunderstorms. The extreme northern portions of the Persian Gulf (including Riyadh, Kuwait, and Basrah, as well as theareaoftheZagros SEA SURFACE CONDITIONS, Persian Gulf, mountains southward toBushehr)will experience a rare mid—levelthunderstorm associatedwith Water currents generally circulate counter- weak troughs in the westerlies. These are most clockwise.As mentioñd earlier, shallow water common during June and July;all are associated in the gulf is due to evapOration and an almost withtroughsin an enhanced and southward— total lack of water flowing off the land.Since depressed high-speed current in the mid-latitude' the water levelis lower than the Gulf of Oman, westerlies, These thunderstorms are similar to a steadyflowofsurfacewaterentersthe thosein the southwestern United States; bases Persian Gulf through the Strait of Hormuz.This are high (above 8,000 feet——2,500 meters) ,with surface current flows west, then northwest,as virga and associated downburst phenomena. it hugs the Iranian shore,At the northern end oftheGulf,itturnstothesoutheast and Isolated thunderstorms can form over the parallels the Arabian coast. Finally, it turns southernZagrosMountainsalongand inland of north along theOmani Peninsulato join fresh the Iranian coast,This activity results from Gulf of Oman water entering through the Strait

44 of Hormuz, Speeds arelessthan 1 knot. latespringandearlysuimner, Surface water Maximum calculatedspeedfor a 100—year worst temperaturerangesfrom82-85°F (27—29°C) In caseof bothwind andtidalcurrents, was 8 June to 90-92°F (42—43°C) In August before knots at Jubail,As water increases in density, droppingto 84—87°F (29-31°C) in September. itsinks,turnssoutheastward,andflows back Temperatures in extremely shallow coastal waters into theGulfof Oman as a bottomcurrent reach 104°F (40°C) on July and August through the Strait of Hormuz, 85% of all wave afternoons. Available temperature soundings In heights average less than 6 feet. Predominant the western Persian Gulf show a bottan direction along the Arabian coast is, as might temperatureof73°F (23°C) at 195 feet(60 be expected, from 330 through 360 degrees. meters). Temperatures show a steady and gradual decrease between the surface and the bottom of Water Temperatures, The temperatureof the about13°F(7°C). Thereis no evidenceof shallow Gulf water here increases rapidly during thermocl ines.

45 THE STRAIT OFHOWIUZ--SO1JTHWEST MONSOON

NESOSCA(.E SThOPTIC FEATURES. The mesoscale Shamal ,windsalongthenorthshoreofthe features that affect the Persian Gulf proper and Strait are northeasterly to easterly during the theGulfof Oman alsoaffecttheStraitof night and earlymorning, and southerlyto Hormuz; there are no known mesoscale features westerlyduringlate morning and afternoon, peculiar to the Strait itself, Alongthesouthernshore,"normal'windsare southwesterlytowesterly eastof theStrait TYPICAL WEATHER. The following weather conditions during the night and earlymorning, and may be expectedinthe Strait of Hormuz during southeasterly tosoutherly west of theStrait. the Southwest Monsoon: Inlate mornings andafternoons, strong southwesterly to west—northwesterly sea breezes blow GeneralSensible Weather overthestrait during alongtheOmani shore westof the Straitand the Southwest Monsoon season consists of patchy northerly to northeasterly east of the Strait. lowstratus and stratocumulusoccurring most frequentlyinlateevening andearly morning. Thunderstorms, Isolated thunderstorms occur over OnshorecloudoccursonlyalongtheIranian theinterior Zagros mountains; they are very coastin theveryshallowSouthwest Monsoon rarely foundin late afternoon over the higher air.Visibilities average 5to 7 miles in dust Omani ranges. None have actually occurred over and salt haze. weather reporting stations. Bases are estimated at4,000 to 5,000 feet(1,200 to 1,SOOm)MSL; Sky Cover. During incursions("pulses') of tops at 40,000 to 45,000 feet (12.2 to 13,7 km), Southwest Monsoon air into the southern Persian Gulf, thunderstorms occur along the mountains on Precipitationisconfinedtotherarethunder- both the Iranian and Omani shores, Bases range storm. No statistics are available, but rain- from 2.000 to 3,000 feet (610 to 915 m); tops fallamounts of 0,5to 1 inch(12 to 25mm)in reachabove45,000feet(13,7km). British thehighermountainsareprobable, Heavier meteorologists stationed at Abu Dhabi and Dubai amounts have cauted flash floods. havereportedseeingthesethunderstormsover theOmani mountains. Unconfirmed reports have Air Temperatures. Maximum temperatures along the been receivedof mountainflashfloods during imediateshore oneitherside oftheStrait such 'pulses." average from 90 to 95°F (32 to 35°C). Minimums average from 80 to 82°F (26 to 27°C) . Tempera- Dustisadvectedintothe Strait of Hormuz from tures inland are modified by increased elevation the Persian Gulf. During strong "Summer and the diminishing sea breeze, Shamals'in the Gulf, visibilities may drop to less than 3 milesinthe Strait,Visibilities below 1 mile——though rare——have occurred, almost SEA SURFACE CONDITIONS. Strait of Hormuz, always associated with near zero visibilities in thesouthernPersianGulf caused by extremely Water currents through the Strait consists of a strong "Summer Shamals." tidal ebb and flood, Duringebbconditions, currentsoflessthan 1 knotflowfromthe Winds reflecta combination of weak inflow from Persian Gulf through the Strait into the Gulf of theGulf of Oman,pronouncedland—sea breezes Oman, During flood tide, currents of less than (especiallyalongtheIranianshore) , and a 1 knot flow from theGulf of Omanthrough the general easterlytosoutheasterlyflow around StraitintothePersianGnlf. Wave heights thesouthern end of theinducedleesideGulf average less than 2 feet (O.6m). low. Complicatingthis patternisthe venturi effect through the narrowest partof the Water temperatures are similar tothose foundin Strait,Precise data for the Strait itself is thePersianGulf. They increasefrom 85—86°F not available, butit appears that wind speeds (29-30°C)inJuneto 90—91°F (32-33°C)inJuly herearedirectlyrel atedto "Summer Shamal" and August. Temperatures fallto 86—87°F (30— strength over the centralandnorthern Persian 31°C)in September. Gulf.In the absence of a well-developed

46 THE GULF OF 0*4% ANDADJACENTLAND AREAS--SOUTHWESTMONSOON

*SOSCALE SYNOPTIC FEATURES. August. The normal land breeze is reinforced by the'fallwind"effect of thehigh mountains The Gulf of Oman low is a result of: thatbacktheirmnediatecoast. Windson the coastclosertotheStraitof Hormuzshow a Terrainfeaturesandcoastline orientation of marked land—sea breeze circulation, Macroscale both the Iranian and the Omani shores gradients irrvnediately southeast of the Strait of Ilormuz are extremely weak. As aresult, night Theposition of theMonsoon Trough/ITCZalong and earlymorningwindsaresouthwesterlyto the Omani mountains-Strait of Hormuz westerlyat 4 to 6 knots; latemorning, afternoon, and earlyeveningwindsareeast— The cyclonic eddy from the main Southwest northeasterlytoeasterlyat 8 to 12knots, Monsoon current. This eddy effect issimilar to Over the Gulfof Oman itself, winds turn theonefoundin summer alongtheCal ifornia southeasterly and increaseinspeedmarkedly coast from Santa Barbara west to Point during daylight hours as the Strait of Hormuz is Conception. approached. Night winds along the Iranian shore east of the Strait and over the northern Gulf of Oman tendto bevariable duetothe opposing TYPICAL WEATHER. Typicalweather conditionsin influences of the land (mountain) breeze and the and near the Gulf of Oman during the Southwest gradient winds. Averagewindspeedsincrease Monsoon are: from less than8 knots just east of the Strait of Hormuz to13—14 knots as the Arabian Seais GeneralSensible Weather overtheIranian coast reached, Surface winds over the southern half andtheopenwatersoftheGulf consists of of the Gulf of Oman and on the Omani coast are patchy low clouds with bases from 1,000 to 1,500 westerly towest-southwesterly (downslope)at 4 feet (305 to 460 m) and tops of 2,500 to 3,500 to 8 knots at night.The sea breeze establishes feet (760 to 1,070 m). From early through late shortly after O900L and persists through morning, ceilings of 800—1,200 feet are coiTmion 1900L. This onshoreflowisnortheasterly to alongthe irmmediatecoast and justinland, easterly and reaches peak speeds of 15—20 knots Visibilities alongthe shore range from 5 to 7 in late afternoon. miles,but over open water,from 7 to 10 miles, Salt haze and dust arethe main Thunderstormsarenormallyonly found in the restrictions. The Omani Coastnormally has highermountainsonboththeIranianand the clear skies, with visibilities ranging from 6 to Omani coasts; these very Isolated storms have 10 miles indust and suspended salt haze. the usual high bases.On rare occasions, there Patchy low clouds form over the inmiediate coasts iswidespreadthunderstormactivity(withlow just after dawn about a third of the time, but cloud bases and heavyrainshowers) overthe skies clear rapidly with morning heating. northern Omani mountains and the Zagros ranges immediately north of theIraniancoastasfar SkyCover. Undertheeffectsof a Southwest northwest as Bandar-e—Lengeh. This activity is Monsoon "onset vortex"ortropicalstorm,the caused bya rare strong pulseinthe southwest usual multilayered low, middle, and high clouds monsoonthatcombineswiththeapproachof a are found overanarea within 300 miles of the weak upper-airtrough overthePersianGulf. storm track orlandfall, But,ashas already This combinationadvects low—level monsoon air been discussed under Transitory Synoptic from overthe Gulf of Oman and theStrait of Features," these storms rarely enter the Gulf of Hormuz intotheextreme southeasternPersian Oman or make landfall on either shore.The rare Gulf. occurrence hereisinJune or early July, but one was observed in August. Precipitation. The onlyprecipitationof any significance is from the rare tropical 3ust. Dust and salthazeare normally present disturbancestrongenough tomake ittothe here, restricting visibility to 5to10 miles. coast. Dieprecipitation canbe heavy——a bit Lower visibilities areonly foundduring a less than 15inches (J8Ormni)wasrecorded in one strong "Summer Shamal ,' Dustraised bythe stormthat made landfall. Extensiveflash Shamal has been observed on satellite imagery as flooding hasalso been reported. fareast as the centralGulf of Oman, Lowest known visibilities(in extreme cases) were AirTemratures. AlongtheIraniancoastand observedas lessthan 3 miles,butthen only overtheGulfof Oman, maximum temperatures briefly. range from 92°F (33°C)in June to 88°F (31°C)in September. Dew points drop from 18°F (25°C)in Winds. A complexwind pattern resultsfrom the Juneto 73°F(22°C)inSeptember. Along the interactionoftheGulfof Oman lowand the Omanicoast,maximum temperaturesinJuly and pronounced land—sea breeze, Iranian shore winds August are 95 and 91°F (35 and 33°C); dew points are east—southeasterly at 9 knots in July and average 70 to 75°F (21 to 23°C).

47 SEA SURFACE CONDITIONS, Gulf of (Ran.

Water currentsintheGulf ofOman maintain a Water temperatures decrease from 86°F to 90°F (30 cyclonicgyre,reflectingthelow—level wind to 32°C) at the Strait of Hormuz to 82—84°F (27- pattern. Speed averages 1 knot. Wave heights 29°C) at the eastern end of the Gulf of Oman. average 4 to 6 feet.

48 THE (SIANIARABIAN SEA COAST--SOJJTIfEST MONSOON

NESOSCALE SYNOPTIC FEATURES. None have a direct gusts.After clearing, speedsincrease to15 to and specificaffect ontheOmani Arabian Sea 25 knots, with higher gusts. Overwa terwinds coast. beyond 25 to 30 miles offshoreaverage 20to 30 knots, with some gusts above 30knots

TYPICAL WEATIER. The following conditions are to Thunderstoras occur over the interio r Oman i be expected in the Omani Arabian Sea Coast mountain ranges in the northeast and the during the Southwest Monsoon: southwest,butthey areprimarily confinedto those rare occasions when pulses in the GeneralSensible Weather. Extensivenightand southwest monsoon current are strongenoughto morninglowclouds(bases from600to1.500 force moist tropical air inland to the feet, tops between 3,000 and 4,500 feet) mountains. increase rapidly after mid—June along the coast and inlandabout50 miles. Seaward extentis Precipitationalongthecoast and offshoreis beyond 100 miles from the shore. These clouds confined,to drizzleunderneathstratocumulus occurafterthefullonsetoftheSouthwest decks. Amounts are lessthan0.05 inches Monsoon and establishment of the Monsooh (1mm) Weather records for the interior are not Trough/rTCZ inlandofthe Omani Arabian Sea available,butreportsofrareflashfloods coast. Low cloud occurrence decreases rapidly suggest that precipitation there can be heavy. aftermid—September as theSouthwestMonsoon weakens and the Monsoon Trough/ITCZ shifts Air Temperatures. There is a distinct moderation south. The greatest occurrence of low cloud is intemperature. The highest temperatures occur on thesouthwesternpartofthe Omani coast inMay and June before the onset of the stratus properduringJulyand Augustnearestthose season (July through early September) . Although regions of theArabianSeawith thestrongest Salalah (17°N, 54°E)is outside the area of this upwelling, or approximately abeam Salalah. study,itstemperaturesarerepresentative of Here,stratus ceilingsliftfroe 600to1,000 thoseinthe Omani—Arabian seacoast's 'stratus feet (180 to 300m)before dawnto become 2,000 area.' Salaiah's maximum temperaturesinJuly to3,000 feet (610to915m) by mid—afternoon, andAugustaverage 81—82°F (27°C); minimums Low ceilings persist over the coldest water off- average 74-75°F (23°C). Masirah (20°41'N, shore for a distance of 50 to 75 miles from the 58°53'E) ,100 milessouthwestof RasalHadd, coast, Drizzle inthe predawnhoursoccurs has a much lower lowcloudfrequency,with nearlyhalfthe time. Low cloudceilings resulting higher temperatures; maximum decreaserapidlythecloseronegetsto Ras temperatures average 86—88°F(30—31°C) inJuly al'Hadd, due to decreased upwelling;low clouds and August. Thumrait (17°40'N, 54°02E) can be dissipate onshore after 0900L.Skies are nearly consideredrepresentative of inlandareas even cloudless beyond 50 miles inland. thoughitissouthwestofthestudyregion. Maximum temperatures here average between 104°F Sky Cover. Pulsesin thesouthwest monsoon (37°C)in June and 95°F (33°C)in July. temporarilydeepen themaritimemoistlayer. Under theseconditions,maritimeairforced onshore canresultinisolatedthunderstorms, SEA SURFACE CONDITIONS. Northwestern Arabian Sea. layeredclouds,andlow ceilings over the main Omani mountain range that leadstowardthe Water currentsare southwesterlyat 5 to 10 Straitof Hormuz, Theselateafternoonand knots. Highestcurrentspeedsareabout 60 earlyevening summer thunderstorms overthe miles offshore, mountains southwest ofAbu Dabiand Dubaihave been observed by British meteorologists at both Water temperaturesinJune, before fullonset of stations and are not unusual, theSouthwestMonsoon,averagebetween 80 to 82°F (27°C). By late June, upwelling in Dust, Blowingdustiscommonalongthenorth- responsetotheSouthwestMonsoon has dropped eastern coast. Strong Southwest Monsoon winds temperatures markedly. During July and August, pick up enough dust and sand to reduce visibili- surfacewatertemperatures average 77 to78°F ties toless than 3 miles onIday out of3. (24to25°C)atRas alHadd. They decrease Weather observations over theinterior of this dramatically to 68 to 70°F (20 to 21°C)at the regionarenotavailable,butsuspendeddust intersectionofthecoast and 20°N. Water that restricts visibility to7 to 10 miles has temperaturesatSalalahareevenlower—-about been reported by oil company exploratory teams. 65°F (near 18°C). The coldest water throughout this portion of the Arabian Seaisinmiediately Winds beneathcoastalstratusandstratocumulus offshore. decks average 10 to 15 knots, with higher

49 Chapter 7

THE FALL TR.4NSTTION (October--Noveirter)

MAJOR CLIMATIC CONTROLS

FLOW PATTERN REVERSAL. Likespring, TheFall and immediate coastlines, Thesestorms bring Transition is a period of major synoptic pattern multilayeredclouds, poorvisibilities,heavy reversal. Althoughthecompletetransition rain, and embedded thunderstorms. Turbulence averages 30 to 45 days, actual onset and ending overcoastalmountainsisintensified, Flash vary by station location andfrom one yearto floodsarepossible. Figure 36 shows mean the next, The change can be very rapid. See tropical storm tracks for October and Movember. Chapter 3.

WEAK LOW—LEVEL CONTINENTAL ANTICYCLONESreplace the massive heat lows of the Southwest Monsoon. Surfacehighpressurecentersare typicallylocatedin• southern Saudi Arabia, central Iran and northern Africa.

STRONG UPPER—LEVEL WESTERLIES delineate the northern extent of the Subtropical Ridge centered near 15°N. Core speeds between 30,000 and 40,000 feet range from 60 to 75 knots. The subtropicaljetisnow centered justsouth of theHimalayasoverIndia. Variationinthis upper-level flow comes from the infrequent appearance of the Polar Jet, Jet maxima of 40 to 60 knotswill move southeastwardwith a cyclonic disturbance from the Mediterranean.

MEDITERRANEAN CYCLONES andtheir associated cold fronts begin to penetrate into the Persian Gulf by mid-November as the Mediterranean storm track begins to reestablish itself.

A WEAK KID—LEVEL TROUGH inthe northern RedSea area acts as a steering mechanism and helps to Figure 36. Mean Tropical Storm Tracks--October shiftMediterraneancyclonesintothePersian and M,venter Cotined. Gulf. The trough becomes a persistent mid—level feature throughout the winter months. SEMIPERMANENT SUDAN LOW, Late in the Fall THE MONSOON TROUGH/INTERTROPICAL CONVERGENCE ZONE Transition, this low acts as a source region for (ITCZ) retreats southward from theextreme cyclogenesis associated with upper—level troughs southeastern part of the Arabian peninsula and in the westerlies. As thesetroughs move theArabian Sea coastofIran and becomes southeastward from theMediterranean, they may orientedeast-northeasttowest-southwestnear triggera transient low center that moves east— the equator. northeastward into the northern Arabian Peninsula, TROPICAL CYCLOIES can form in the Monsoon Trough/ITCZwhileitisstillnorthof10'N. MEAN OCTOBER FLOW at 850, 700, 500, 300, and 200 These rarelyeffectthePersianGulfregion, mb,(5,000,10,000,18,000, 30,000,and 39,000 averagingonly one occurrence every10 years. feet)are shownin Figures 37,38, 39, 40, and The primary area affected is the Gulf of Oman 41.

50 25°E 40°F 60°E 80°E

30° N

200 N

10°N

Figure 37. Mean October 850mb Flow.

25°E 400 F GOOF 80UE

300 N

20N

10°N

Figure 38. Mean October 700mb Flow.

51 25°E 40°E 60°E 80°E

30° N

20°N

100 N

Figure 39. Mean October 5OUmb Flow.

25°E 40°f 60°E 80°E

30° N

20°N

100 N

Figure 40. Mean October 300mb Flow.

52 25°E 40°E 60°E 80°E

30°N

20°N

10° N

Figure 41. Mean October 200mb. Flow.

53 TRANSITORY SYNOPTICFEATURES--FALLTRANSITION

WEAK UPPER—LEVEL TROUGHS in the westerl ies trigger a secondarytransientlowinSudan. normally begin penetrating southward through the This combination often resultsin cyclogenesis Persian Gulf Region by mid-November, often and frontogenesis in the Arabian Peninsula, The accompanied bytypical surface pressure and secondarylow becomes thedominant pressure frontalsystems, Associatedweatherincludes center and tightens the pressure gradient in the sand and dust storms, squall lines, and PersianGulf, Coldairadvectionoverthe thunderstorms throughout most of the region. At mountains of Turkey and Iran can drive the cold least one severe squall line can be expected to front as farsouth asthenorthernArabian move southeastward down the Persian Gulf during Sea. The rate of progress of the Winter Shamal this period, isdirectly dependentonthe movementof the upper-level trough, Typically theseearly "WINTER SHANALS" are strong northerly or Shamals last 24to36 hours. However,if the northwesterly windsthat can begin inmid- upper-leveltroughstallsneartheStrait of November, This phenomenon is often the result Hormuz(dueto a strengthening ridgeeastor ofintensificationof a cyclone(or'low') another low forming to the west), the Shamal may movingeast-southeastwardoutoftheeastern lastfrom 3 to 5 days, For a more detailed MediterraneanIntoSyria. As theupper-level discussion, see Chapter 4, The Northeast trough moves into the Arabian Peninsula it may Monsoon,

54 THE PERSIAN GULF AXE) AIJJACENT LAND AREAS--FALL TRANSITION

NESOSCALE SYNOPTIC FEAIURES. Land-seabreezes Arabia and Iraq, The strong northwesterly low— become increasingly important as they become the level winds are then quicklyreinforced by predominant feature along coastlines during northwesterly upper-level winds behind the undisturbed(normal")conditions. Gradient upper-leveltrough. Theassociatedupper-air wind direction and speed areoftengreatly troughs are almost always rapidly moving short modified by land-sea breezes. The effects are waves during this transition;surface winds die greatest nearcoastlineswithsteep terrain after24to36 hours. Speedsinsuchcases grad i en ts, typically reach 30to40knots. For a nmre detaileddiscussion, see "WinterShamals" in TYPICAL WEATHER. The following weather conditions Chapter 4, "The Northeast Monsoon." may be expectedinthePersianGulf andits adjacent land areas: Thunderstorms. Thunderstormsoccuralong and ahead of cold fronts moving southeastwarddown GeneralSensibleWeather. Patchyhighclouds theGulf. Severethunderstormsoccasionally (mean coverage 1/8) and unrestricted visibilties occur with cold fronts or squall lines. Themain become the rule. area affectedis the central and southernGulf and itsinrediatecoastlines. Thundersto rm SkyCover. The only cloud cover of significance winds above 50knots have been recordedinthe isthatcausedby low pressure systems or the United Arab Emirates.Although surface hailhas interaction of Subtropical and Polar jet notbeen reportedovertheGulf oralongits streams. The lows move intotheareafrom immediate coasts, it has been reported withsuch eastern Europe or the Mediterranean.Clouds are storms over the Omani and Zagros Mountains. usually middle andhigh; scatteredareasof 2,000-3,000ft (610—915m) ceilings and rain- Precipitation shows a dramaticincreaseinthis showers occur in the southwesterly flow ahead of areaastheseasonprogresses. TheSiberian the low. Isolated 1,SOOft (460m) ceilings occur Highstrengthensas the upper—levelwesterlies withrainsqualls and thunderstorms inthe build; this combination shifts a storm track iimnediatevicinityofthelow and itscold southward into the PersianGulf. Average front. Such systems are relatively weak, amounts of less than 0.25 inch (6mm)increase to affectingareaweatherfor 24—36 hours. The between0.75 and 1.00inches(19 and25mm) by Subtropical and Polarjetstreamsinteraction November. Most of the increased precipitation over the Arabian Peninsula often resultsin two falls over the Zagros Mountains. distinct cirrus bands that are easily discern- ible on satelliteimagery. One bandcurves Air Temperaturesdrop significantly. Daytime cyclonicallywiththePolarJet; theother maximum temperatures alongtheimmediate coast turns slightly anticyclonically with the cooltobetween 85 and 95°F(29 and 35°C). Subtropical Jet. Strong wind shear near the jet Inland, temperatures decrease even more dueto maxima are likely to produce complicated the significant loss of solar insolation and the vertical and horizontalturbulencepatterns. strengthening of continental anticyclones. The Terrain features can further compound turbulence Zagros Mountains bear the bruntof these patterns. changes; maximum temperaturestherefallto lessthan80°F(27°C)nearShiraz and Jahram, Dust. Blowing dust and sand frequencies decrease Minimum coastlinetemperaturesaverage 55 to sharply as the season progresses. Average 65°F (13 and 18°C) Inland temperatures can fall visibilitiesrise dramatically to above 7 to below 45°F (7°C), again at Shiraz and miles. Thenorthwestern shore of the Persian Jahram. Dewpoints on both coasts of the Persian Gulfmaintains a higherincidenceofblowing Gulf drop tobetween 45and 55°F(7 and 13°C) dust andsanduntilthe first significant rain during this period. Inland, dewpoints fallto because of the extreme dryness of its very fine between 35 and 45°F (2 and 7°C). soil. The occurrence of blowing dust and sand is tied to strong convective activity associated with increasing numbers of cold fronts passing SEA SURFACE CONDITIONS. Persian Gulf. through the area. Water currents show a generalcounter-clockwise Winds remainnorthwesterly,butspeeds decrease. circulation. Shallow water levels are dueto Winds back from the northwest tothe southwest evaporationandanalmosttotallack of water ahead of troughs or cold fronts moving into the flowingoffthelandintothePersianGulf, regionfromIraq. Windsturnwesterly,then which is lower than the Gulf of Oman. southerly, as one approaches theStraitof Consequently, a steadyflowofsurface water Hormuz. Speeds are stronger on the Arabian side enters thePersianGulf through theStrait of of theGulf(10—15 knots); theIranian coast Hormuz. This surface current flows toward the averages 5—10 knots. The 24— to36-hour west and then northwest asit hugs the Iranian sustainedhighsurface winds characteristic of shore. Atthenorthernend oftheGulf,it "Winter Shamals" begin in November. Large turnssoutheasterlyto paralleltheArabian pressuregradientsdevelop behindcoldfronts coast. Finally,itturns northerly alongthe due to upper—level subsidence thatrapidly Omani Peninsula to join fresh Gulf of Oman water builds surface high pressure over western Saudi entering through the Strait of Hormuz,Speed is

55 less than 1knot. Maximum calculated speed for Water Te.jratures. By November, water a 100—year worst case of bothwind andtidal temperaturesrangefrom 80 to82°F (27 and currents was 8 knotsatJuball . As water 28°C). They are actually afew degrees higher Increasesindensity,itsinks,turnssouth- thanthe mean airtemperature. Watertemp- eastward, and flows back into the Gulf of Oman erature soundings show a temperature decrease of as a bottomcurrentthroughtheStraitof 10 to 15°F (6 to 9°C)in the upper 195 feet (60 Hormuz. m) of the Gulf,

56 THE STRAiT OF HOsTIUZ--FALL TRANSITION

NESOSCALE SYNOPTIC CONTROLS. Land-seabreezes are point, Strongest winds continue tobe on the Increasingly important here as they become the southern coast with speeds of 10—12 knots from predominant feature along coastlinesduring the northwest. Winds on the Iranian coast, as undisturbed("normal") conditions. Gradient reflected by Bandar Abbass observations, winddirection and speed areoftengreatly continue from the south at 7—8 knots. modifiedbytheadditionofland—sea breezes, These effects are greatest near coastlines with Thunderstormsoccurwithsqualllinesahead of steep terrain gradients. coldfrontsorwithcoldfrontal passages. Although still rare, thunderstormfrequency increasestowardstheendofNovember asthe TYPICAL WEATHER, The followingweather conditions Mediterraneanstorm track becomes established. areto be expectedintheStraitof Hortnuz Bases are between 2,000 and 3,500 feet (610 to during the Fall Transition: 1,070m); topscanreach45,000feet(13.8 km). Isolated thunderstorms——usually associated General Sensible Weather during normal conditions with squall lines——may approach, or even exceed issimilartothatoftheSouthwestMonsoon, severe limits. Patchyearlymorninglowstratusand stratocumulus ceilings decrease on the southern Precipitation increasesdramatically. Average coast; percent frequencies drop from 15-20% in amounts of less than 0.25 inch (6mm) increase to Augusttoless than5% bylateOctober. The between0.75and1.00inches(19and 25m)by northern coast still sees upslope conditions due November, Higher amounts (up to 3 inches——7Smm) tothe mountains limiediately inland; frequen- occuroverthe ZagrosMountains,almostall ciesdecreasemore slowly, Forexample,at associatedwith prefrontaland frontalshowers Bandar Abbass, Iran, ceiling frequency continues and thunderstorms. to average 15-20% during October, but drops to near 10% in November,Visibilities, except with AirTemperaturesalongtheimmediateshore on thunderstorms and precipitation, are excellent, either side of the strait average 85 to 90°F (29 and 32°C) , Minimums drop to between 65 and 70°F Sky Cover, Middle and high cloud ceilings occur (18 and21°C). Temperatures inland are cooler ahead of and during the passage of low pressure because of increased elevation, centers. Ceilings of 2-3,000 feet (610 to 915m) andvisibilities of 3—5miles (5—8km) inrain showers are confinedtotheirmnediate vicinity SEA SURFACE CONDITIONS, Strait of Hormuz, of the low. Water currents through the Strait consist of tidal Dust.Blowingdustorsandvirtually disappears ebb and flood. During ebb conditions, currents after the first rains of the season.The rare of less than 1 knot flow predominantly from the blowing dust that is seen has been advected from Persian Gulf through the Strait into the Gulf of the Persian Gulf, 0mn. During flood tide, currents of less than 1 knot flow from the Gulf of Oman through the Winds, except during low pressure center passages, Strait into the Persian Gulf. resemble those foundinthe Southwest Monsoon. Thisflow resultsfrom a combination of weak Water temperatures are similar tothose foundin inflowfromtheGulfof Oman andpronounced thePersianGulf. Seatemperatures coolfrom land-sea breezes, especially along the Iranian between 85 and 87°F (29 and 31°C)in October to shore. Theventurieffect through the narrow between 81 and 82°F (27 and 28°C)in November. part of the Strait increases wind speeds at that

57 THE GULF OF OMAN AND AD.JACEFIT LAND AREAS--FALL TRANSITION

NESOSCALE SYNOPTIC FEATURES. •Land-sea breezes are higherZagrosand Omani Mountains, Isolated increasingly important as they become the severe thunderstorms are possible overthe predominant feature along coastlinesduring latter. normal conditions. Gradient wind direction and speed are often greatly modified by the addition Precipitation shows a dramaticincreaseinthis of land-sea breezes,These effects are greatest area as the season progresses, Average amounts near coastlines with steep terrain gradients. increasetobetween 0.75 and1.00inches (19— 2simn)by November. Precipitation from the rare tropicalstormisenhancedover the mountains TYPICAL WEATHER, The following weather conditloAs inland of the coasts. Exact rainfallrecords areto beexpectedintheStraitof Hormuz are not available, bUt 10 to15inches (255 to during the Fall Transjtion: 380nm)has been reported with spring and suimner tropical storms. Rainfall overthehigher General Sensible Weatherinthis areais nearly mountainscould be in excessof 20 inches always good. Except for wispy cirrus, skies are (SlOimn) clear and visibilities excellent, Air Temperaturescool gradually,butnot as Sky Cover, Patchy middleandhigh cloud decks rapidly as along the shores of the Persian Gulf occur with the infrequentbut increasing numbers and inland over theArabian Peninsula and oflow pressurecentersandassociatedfronts rran, Diurnal ranges, on theotherhand, that move through the Persian Gulf to the Gulf increase markedly. These go from 5to 10°F (3 of Oman near the end of November, These rare to 6°C) at the end of September to 10 to 15°F (6 lows originate in Eastern Europe or the to 9°C) by November. Temperatures on the Mediterranean. Multilayeredlow,middle,and Iraniancoastarecoolerthanthose on the high clouds occur with the rare tropical cyclone Arabianside of theGulf of Oman duetothe asitmoves westward out of theArabianSea. effectsof the Zagros Mountains. Maximum Occurrence of tropical cyclones inthis area is temperaturesarebetween80 and85°F(27and lessthan 1% inanygivenyear, Theusual 29°C)northandbetween85and 90°F(29and weather conditions (lowceilings and visi— 32°C) south.Minimum temperatures range from 70 bilities, heavy rain, and,in very rare cases, to 75°F (21 and 24°C) north and from 75 to 80°F huricaneforcewinds) may occurwiththese (24 and 27°C) south. systems.

Dust is almost nonexistent untilthe first 'Winter SEA SURFACE CONDITIONS, Gulf of Oman. Shamal ,° inlateNovember, Eventhen,visi— bilities normally remain above3 miles, Water currents slowly reverse (from the southwesterly and westerly flow of late Windsarepredominantly land-seabreezes. The September toeasterlybylate November) and mountainsthatriseininediatelyinland of the reflectthechangeinmonsoorialflow. Speed coast on the western side of the Gulf of Oman averages 0.4 to 0.7 knot, give such winds increased strength, Mean wind speeds drop throughout the area, averaging 5to Water temperatures coolslowly. However,asin 8 knots east of the Strait of Hormuz. Stronger the Persian Gulf, mean sea surface temperatures winds areassociatedwithincreasedpressure becomeIto 2°F (0.6 to 1.2°C) warmer than mean gradients south of t low pressure center in the air temperatures,Average sea temperatures cool Persian Gulf, from between 82 and 85°F (28 and 29°C) in October to between 80 and 81°F (27°C) in Thunderstons are confined to passages of November. prefrontal squall lines and cold fronts over the

58 THE &IANJ ARABiAN SEACOAST--FALL TRANSITiON

MESOSCALE SYNOPTIC CONTROLS, Land-sea breezes are southwesterlies end withtheretreatofthe increasingly important as they become the Monsoon Trough/ritz southward.Behind it, winds predominant feature along coastlinesduring switch to and steady at north—northeast. Speeds normal conditions, Gradient wind direction and decrease to between 7 and 10 knots. speed are often greatly modified by the addition of land—sea breezes.These effects are greatest Thunderstorms are very rare, occurring only in the near coastlines with steep terrain gradients. high Omani mountains in late November, and only with the passage of Mediterranean cold fronts. TYPICAL WEATHER. The following weather conditions Precipitation isfound onlyinthe high mountains areto be expectedon the Omani Arabian Sea in late November with the rare frontal Coast during the Fall Transition: thunderstorm, No rainfalldata is available, General SensibleWeatherimprovesdramatically, Air Temperature.With virtually clear skies, mean Therearenormallyonlypatchyhighclouds; maximum temperaturesinOctober'rise 1 to 2°F visibilities are unrestricted. (0,6to1.2°C)to 87-88°F (31°C). Conversely, October minimum temperatures coolto between 68 SkyCoverrapidlybecomes 1 to2/8cirrusand and 72°F(20and 22°C) , November temperatures cirrostratus. Flow from the northeast causes a coolstillmore. Maximum temperaturesrange dramaticreductionintheupwelling of cooler from 78to 82°F (26 and 28°C) while nights cool waters along the Omani Coast and eliminates the to 63—67°F (17-19°C). stratusand stratocumulusdeckscharacteristic of the Southwest Monsoon. SEA SURFACE CONDITIONS, Northwestern Arabian Sea. Dust ceasesto be a problem as winds become northeasterly andspeeds drop drastically from Water currents remain southwesterly until onset of those of the Southwest Monsoon, The changein thefullnortheast monsoon. Speeds,however, wind direction during this period shuts off the decrease to3 toS knots by late November. Wave source of the blowing dust or sand, Occurrences heights average 3 to 5 feet. at Masirah, for example, decrease from 8—12 days during September to zero by late October. Water temperaturesriserapidly as upwelling ceases. Mean temperatures are 81°F(27°C)by Winds alongthecoastandoffshorereflectthe early October and remain warm throughthe strengtheningoftheNortheastMonsoon behind season. the Monsoon Trough/ITCZ.The sustained, strong

SI BIBLIO&%IP4Y

Ackerman, S,A., and Cox, S.K., "The Saudi Arabian Heat Low: Aerosol Distributions and Thermodynamic Structure,' Journal of Geophysical Research, Vol. 87, No, cli, pp. 8991-9002, 1982.

Al—Jerash,M.A.,"ClimaticSubdivisionsinSaudiArabia: An Application of PrincipalComponent Analysis,Journal of Climatology, Vol 5, pp. 307—323, 1985. Al—Shalash, A.H.. Rainfall Maps of the KingdomofSaudi Arabia, 1973.

Al—Zaheri, M.S., and B.N. Charles, "A Cloud—Like FeatureinSatellite Imagery of Saudi Arabia," The Meteorological Magazine, Vol. 112,No. 1326, pp. 65—68, 1983

Blackand Vetch,Geological, Meteorological,and LocationalReference Data for UseintheSaudi Arabian Design and Construction Program, Special Study, 1976. Clark, D.J.,Pressure Jump Lines in the Persian Gulf.' The Meteorological Magazine, 1968. Climate and Weather of the Arabian Peninsula, AWS/FM—100/09, HQ Air Weather Service, Scott AFB,IL, 1980. Climate and Weather of Iraq, Iran, Afghanistan, AWS/FM-100/12, HQ Air Weather Service, Scott AFB, IL, 1980. Climatic Atlas of Iran, Iran Meteorological Department, 1968. Climatic Study of the Persian Gulf and Gulf of lnan, Naval Oceanographic Coimnand, Near Coastal Zonp, 1980. Climatological Atlas of Iraq, Iraq Meteorological Department, 1960.

Climatological(sic]Suirinaries, KuwaitInternationalAIrport, 1962-1982, Kuwaft Meteorological Department, 1983.

Condray, Patrick M. •and RogerT.Edson, Persian Gulf Transmittance Study In the 8-12 Micron Band, USAFETAC/TN-88/003, 1988. Crutcher, H.L., and R.G. Quayle, "Mariners Worldwide Climatic Guide to Tropical Storms at Sea," NAVAIR 50—1C—61, 1974. Ojavadi, C., "Clmates of Iran," Monographies de Ia MeteorologieNationale, Nr, 54, 1966, AO-B094432L.

Dodd, A.V., "Some Aspects of' the Climate of South—West Asia,'The Meteorological Magazine, Vol.94, No. 1111, pp. 38-47, 1965.

Dust Forecasting——Southwest Asia, AWS Follow—On Training Program, 52674—OF,HQ Air Weather Service, Scott AFB, IL, 1981. Farrell, Robert J,, Jr.,Refractivity Climatology in the Persian Gulf, unpublished study, 1988.

Fett, R.W,, and Bohan, W.A., Navy Tactical Applications Guide. Volume 5, Part 1.Indian Ocean. Red Sea/Persian Gulf.Weather Analysis and Forecast Applications.Meteorological Satellite Systems, NEPRF TR 83-02, AO—A134412.

Fett, R.W. and Bohan, W.A., Navy Tactical Applications Guide. Volume 6, Part 1,Tropics. Weather Analysis and Forecast Applications.Meteorological Satellite Systems, NEPRF TR 86-02.

Flohn,H,,"Synoptic Analysis of the hG DuringSummer,"Studies onthe Meteorology of Tropical Africa, Meteorological Institute of the University of Bonn, 1965. Grant, K.. "A September Monsoon Depression at Masirah, Oman,' The t'feteorologica7 Magazine, Vol. 107, No, 1272, pp. 205-209, 1978.

Grant,K,,. Vector Mean WindsintheLower Troposphere over Arabia and Environs in.Ju7y,Special. Investigations Memorandum No, III, British Meteorological Office, Bracknell, UK, 1983. Houseman, J,, "Dust Haze at Bahrain," Meteorological Magazine, Vol. 90, No. 1063, pp. 50—52, 1961.

60 Hubert, W.E., Hull, A,N,, Morford, D.R., and Englebretson, R.E., Forecasters Handbook for the Middle East/Arabian Sea, NEPRF CR 83—06, AD—A134312.

IMCOS MarinLtd.,Handbook of the WeatherintheGulf Between Iran and the Arabian Peninsula. General Climate Data, 1976.

IMCOS MarineLtd.,Handbook of the Weatherinthe Gulf BetweenIranandthe Arabian Peninsula, Surface Wind Data, 1974, Investigations Division Climatological Report No 104, Iraq, U.K. Meteorological Office, 1960. Investigations Division Climatological Report No 108, Persian Gulf States (Bahrain, Qatar, Trucial States, Oman, and Muscat), Parts I and II, U.K. Meteorological Office, 1962.

Jackson,C.C.E., "VortexPhenomenain the United Arab Emirates," Weather, Vol. 42,No.10, pp. 302- 308. Kuo, W.S., A Study of Weather Over the Arabian Peninsula, 1965. Lighthill, M.J., Sir, Monsoon Dynamics, 1981. Local Forecast Study for Dhahran, Saudi Arabia, 2d Weather Wing, USAF Air Weather Service, 1957. Local Forecasting Studies, Habbaniyah, Iraq, 19th Weather Region, USAAF Air Weather Service, 1945.

LocalForecasting Studies, NasirahIsland,Oman, Arabia,19thWeatherRegion,USAAF AirWeather Service, 1945.

LocalForecasting Studies, Muharraq Island, Persian Gulf,19th WeatherRegion,USAAF AirWeather Service, 1944. Local Forecasting Studies, Salala, Oman, Arabia, 19th Weather Region, USAAF Air Weather Service, 1944.

LocalForecasting Studies,Sharjah,Trucial Oman,Arabia,19th Weather Region, USAAF Air Weather Service, 1945.

Marcal ,G. ,Meteorology of the Persian Gulf and of Several Airports on the Arabian Gulf, Air France, 1980, AD-A157441.. Memberry, D.A., 'A Documented Case of Strong Wind Shear,Weather, Vol. 37, No. 1, pp. 19—23, 1982. Memberry, D.A., "Low Level Wind Profiles During the Gulf Shamal ,' Weather, Vol. 38, No.1, pp. 18—24, 1983. Memberry, D.A., 'A Unique August Cyclonic Storm Crosses Arabia,' Weather, Vol. 40, No.4, pp. 108—114, 1985. Meteorological Memoirs, VolI.,Iraq Meteorological Department, 1962. Middleton,N.J.,"Dust Stormsinthe MiddleEast,'Journal of Arid Environments, 10—2. pp.83—97, 1986. Middleton, N.J., "A Geography of Dust Storms in South-West Asia," .Journal of Climatology, Vol. 6, pp. 183-196, 1986.

Murray, R. andCoultard,G.A,"A Thunderstorm at Sharjah,Persian Gulf, on 23 November 1957," The Meteorological Magazine, Vol. 88, No, 1043, pp. 176-178.

NationalIntelligence Survey, Section 23, Weather and Climate, Iraq, Arabian Peninsula,1970,AD- B052180,. National Intelligence Survey, Section 23, Weather and Climate, Iran, Afghanistan, 1970. Pedgley, D,E., "The Climate of Interior Oman,' Meteorological Magazine, Vol. 99, No, 1171, pp. 29—37, 1970. Pedgley, D.E., "Cyclones Along the Arabian Coast," Weather, Vol. 24, No. 11, pp. 456—470. 1969. Perrone, T.J., Winter Shamal In the Persian Gulf, NEPRF Technical Report 79-06, AD A 077 727,

61 Ranage, C, 'Fjfth Meteorology Training Seminar, Subtropical Cyclones 1, General CharacterlstlCs,' May 1980. Ramage, C., Monsoon Meteorology, Academic Press, NY, 1971,

Route Climatology:Route 3, Adana-Karachi-Peshawar-Adana, Suirmer Season (June - July - August), 19th Weather Region, USAAF Air Weather Service, 1944.

Route Climatology:Route 4, Adana-Teheran-Beirut-Ohahran-Adana, Surener Season (June - July - August), 19th Weather Region, USAAF Air Weather Service, 1944.

Shehadeh, N.A,, DiscomfortinSharjah," Meteorological Magazine, Vol.113,No, 1342, pp.114—120, 1984.

Smith, R.B., "AIPEX:Some Current Issues," Seminar/Workshop 1986:Observation, Theory, and Modelling of Orographic Effects. 15—19 September 1986, Volume 1, European Centre for Medium Range Weather Forecasts, 1987. Snead, R.E., 'Weather Patterns in Southern West Pakistan," Arch. Met. Geooh, Biokl,, Ser. B,16, pp. 316-346, 1968. Soliman, K.H., Air Masses and Quasi-Stationary Fronts in Spring and Suirrner over the Middle East, 1951.

StationClimaticSummaries, Asia, USAFETAC/DS-87/035, USAF EnvironmentalTechnicalApplications Center, Scott AFB,IL, 1987, Stewart, D,A., Essenwanger, 0.M., and Levitt, L.J., Atmospheric Conditions in the Middle East, USANC TR RR—85-3, 1985, AO—A165795.

Takahashi ,K.and Arakawa, H,, 'Climates of Southern and Western Asia,'WorJd Survey of CHrnatology Volume 9, 1981.

Terminal Forecast Reference Notebook, USCENIAF ELF ONE COMMAND, USCENTAF/WE, 1987.

Walker,3.M., "Some IdeasonWinterAtmosphericProcessesOverSouth—WestAsia,"Meteorological Magazine, Vol. 96, No. 1139, pp. 161-167. Watt, G,A,, "A Comparison of Effective Temperatures in Bahrain and Sharjah,' Meteorological Magazine, Vol. 97,No, 1155, pp. 310-314, 1963. Watt, G.A., "An Index of Comfort for Bahrain," Meteorological Magazine, Vol 96, No. 1144, pp. 321-327, 1967. Watts, 0., 'Severe Cyclone in the Arabian Gulf-June 1977," Weather, Vol. 33, No.3, pp. 95-97, 1977.

Weather andIts Effects: Arabian Peninsula Area, AWS Follow-On Training Program, 52517—DF, HQ Air Weather Service, Scott AFB, IL, 1980. Wheather, H.S,, and N.C. Bell, "Northern Oman Flood Study," Proc.tstn. Civ. Engrs, Part 2, 75, pp. 453—473, 1983, Williams,R.O., ARANCO Meteorologic and Oceanographic Oats Book for the Eastern Province of Saudi Arabia, 1979. Wolfson, N., and Matson, N., "Satellite Observations of a Phantom in the Desert," kleather, Vol. 41, No. 2, pp. 57—61. 1986.