December 1964 Raymond A. Green 601

THE WEATHER AND CIRCULATION OF

Abnormal Tropical Storminess

RAYMOND A. GREEN

Extended Forecast Division, National Meteorological Center, U.S. Weather Bureau, Washington, D.C.

1. WEATHER HIGHLIGHTS lantic both low-latitude troughs mere deeper than usual while the subtropical High \vas abnormally strong and Tropical storms were unusually numerous in the Pacific displaced slightly northmard from normal. The distribu- and the Atlantic cluring September 1964. Over the United tion of the height anomaly indicates faster than normal States severe flooding occurred in southern sections while subtropical easterlies. These factors, plus the iiitcraction severe drought persisted in the Kortheast. with short-wave westerly troughs, may account for the was an outstanding feature of weather numerous tropical storins in the Atlantic despite t,he in the United States. In it caused record-break- unfavorable southward position of the mean 700-inb. jet ing winds of S2 m.p.1i. at Jacksonville, tides 4 ft. higher (fig. 3). than previously recorded off St. Augustine, and tides 10 Five tropical storms originated in the Atlantic and ft. above noniial at Mayport. Extensive flooding accoiii- Caribbean in September, wliercas the expected number is panied the storm as rainfall accuniulations exceeded 10 three. Four of these developed to hurricane intensity in. over an estimntecl 10,000 sq. mi. One storni tot,al at (Hilda on October 1). Most of the storins followed paths Mayo, Ha., mas 23.73 in. Only one fiitulity mas directly suggested by the average monthly circulation (figs. 1, 2). attributable to the storm, according to preliminary rc- Hurricanes Ethcl and Gladys (fig. 4) curved northward ports, but property daniwge was cstiinnted at more than through the western Atlantic trough and tropical storm $200 million. Florence stayed in the eastern trough. Hilda formed in Elsewhere in the Nation floods occurred in southern another trough near western . Only the path of Arizona and . At Tucson, Ariz., 3.05 in. of flood- Dora, while west of 7OoW., was apparently unrelated to producing rain fell in 24 hours on the 9-10th. In south- the monthly mean 700-nib. flow. western Texas rainfdl ranged up to 15 in. for 2 days near In the Pacific the subtropicd ridge (fig. 1) and the mid-September causing flash floods in the Rio Graiide 700-mb. height anomaly (fig. 2) were much niore xonitl Valley and serious flooding in the upper Nueces Basin. rind extensire than in the Atltmtic. Tllese c1iur:wteuistice Squall line and frontal showers with totals ranging to and the strong easterly flow in the subtropics (fig. 3) ap- more than 10 in. the next weekend caused further inuuda- parently encouraged the developinen t of tropical storms tions in the Nueces River Basin and floocliug of the Trinity (seven observed against five expected), but inhibited their River Basin. On the 25th locally heavy showers along a recurrature northward. A single typhoon recurved into cold front brought up to 7 in. of rain :ind flooded streets the westerlies (fig. 5) compared to 56 percent expected. in Corpus Christi, Tes. Five-day iiict~n700-mb. charts showing paths of con- Drought continued in the Northeast, where Albany, current tropical cyclones in the Atlantic (fig. 6) reveal N.Y., reported the least September rainfall since records ninny details of the circulation tlmt are obscured iii the began in 1S26, and the sixth consecutive month wit8h mean for September, such as interaction between the subnormal amounts. Northern Cdifornia and the ad- easterlies and wives in the westerlies. During September jacent part of Nevada were also dry with numerous forest 3-7 (fig. 6A) became extratropical iu a fires. Reno, Nev., rcported 99.7 percent of possible sun- westerly trough which was shcaring from the easterly shine for the month. trough containing hurricane Dam. As Ethel appronclied Dora and intensified late in the period, the latter began I. TROPICAL STORM ACTIVITY RELATED TO 30-DAY to curve westward. MEAN AND 5-DAY MEAN CIRCULATIONS By September E!-12 (fig. 6B) an east-west ridge was bridged solidly north of hurricanes Dora and Ethel. Slow Some of the features of the mean 700-mb. circiilation motion, typical near the time of recurvature, occurred for September 1964 (figs. 1, 2) are believed conducive to late in this period; this helps to account for the large the formation of tropical storms (see [l, 21). In the At- rainfall accuniulations with Dora.

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FIGUREl.--h4ean 700-1nb. contours (tens of ft. at 100-ft. intervals) for September 1064. Northward recurvature of tropical cycloiles was favored in the western Atlantic but not in the western Pacific.

FIGURE2.--Mean 700-mb. height departures from normal (tens of FIGURE3.-Mean isotachs (meters per second) at TOO mb for ft., with zero isoplcth heavy) for September 1964. Distribution Scptcmber 1964. Solid arrows indicate principal axcs of niaxi- of height anomalies was conducive to development of tropical mum wind speed and dashed lines the normal. IVcstcrly jet was cyclones. south of normal around most of hemispherc.

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FIGURE4.--Preliminary tracks of Atlantic and Caribbean tropical cyclones during September 1964. Circles (open for tropical storms and solid for hurricanes) with dates indicate 1200 GAIT positions.

FIGURE5.-Preliminary smoothed tracks of Pacific tropical cyclones during September 1964. Circles (open for tropic:Ll storms r211d solid for typhoons) with dates indicate 1200 GMT positions.

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FIGURE6.--Mcan 700-mb. contours and coilcurrent sca lcvel tracks of Atlantic tropical cycloncs for 5-day pcriods: (A) Septeiiiber 3-7, (B) Scptcnibcr 8-12, (C) Septcmbcr 12-16, (I)) -21, and (E) Septenibcr 22-26, 7964. Circles with dates, indicating 1200 GMT positions of stortns, are open for tropical storms, solid for hurricanes.

During the nest period (fig. GC) Dora and Ethel mo\-ed thc strong polar trough, Gladys decelerated and began into the westerlies where they accelerated and became slo\v recurl-ature northward. extratropical; storm Gladys became a hurricane by the The western Atlantic trough extended to the Caribbean 1Gth. High pressure persisted between the trough with from mid-latitudes during the final period (fig. BE) as Dora and Ethel and the easterly trough with Gladys Gladys became extratropical. Hilda formed in thc through the nest period (fig. GD). Though bypassed by cyclonic, region near western Cuba on the 29th (see fig. 4).

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FIGURE7.-Pcrccntage of normal precipitation for September 1964. FIGURE8.--Dcparture of average tempcraturc from rioriiial (OF.) llrought was r elicvcd in so11t h wcs t ern Texas, southeastern for September 19G4. Most of the United States \vas cooler than hfinnesota, and i\fiddlc Atlantic Coast, but continued in the normal. (From [3].) Northcast. (From [3].)

a few days later. Stable waves along slow-moving fronts helped to produce as mucli as twice the normal rainfall for the nionth in part of the Ohio Valley. Moisture transported northmrd from tropical storm Tillie (which 3. CIRCULATION IN THE WESTERLIES dissipated west of Baja Ca1iforni;L) probably contributed Tn the westerlies there were three broad cyclonic regions to the heavy rains in southern Arizona on the 9-10th. with large negative height departures, separated by rela- Hurricane Cleo was responsible for 4 in. of rain in parts tively narrow ridges. Wind speeds south of the large of sout8heastern Virginia on . Excessive negative centers mere faster than normal by as much as precipitation could be expected over the North Central 5 1n.p.s. OR K ewfoundland, 6 1n.p.s. orer northern Russia, States in the mean cyclonic flow, and in parts of the and 8 ni.p.s. south of the Bering Sea. Wind speeds along Southwest with average southerly flow of warm, moist the mean 700-nib. jet were slower than normal only air from the Gulf of mcl the Gulf of . through the strong ridge over , where the circula- Over the Northeast, lion-ever, the average 700-nib. tion is usually cyclonic in September. In general the belt flow was anticycloiiic with respect to normal (fig. 2) of niaximum west winds was observed south of its nornial and drought continued over New York, New England, position :wound the Northern Hemisphere. and parts of Pennsylvanin. Much of the West, with a While the westerlies tended to split in the eastern slight northerly component of anoninlous flow, \VAS dry Pacific and brarch to either side of the Gulf of Alaska, except for spotty precipitation in the mountains. i~ strong connection was kept between the Yukon ridge and the subtropical ridge. Height departures downstream 5. TEMPERATURE were neg:Ltive froin central Mesico to the Canadian Over the United States most temperatures averaged prairies and 2). east\vard to the north-central Atlniitic (fig. below norinal in September (fig. S). This relntively cool pattern IV ns consist en t mi tli negn tiv e height an om dies 4. PRECIPITATION in the West but not with positive height departures from Though rainfall tot8nls with slow-moving Dora were the Ohio Vdey eastward. Recurrent rainfall along large, greater abnormalities of precipitation occurred retarded fronts in much of this region, with associated elsewhere in the United States. At Tucson, Ariz., the cloudiness, could account for the coolness. Cloudy, rainy rccord-breaking total of 5.11 in., and another accumu- weatlier also Iielped to reduce temperatures to the record lation in the Valley, were more than five low average at Tucson, Ariz. (76.3' F.) and at hllissoula, times the normal September rainfall (fig. 7). Other Mont. (51' F.). record high totals were 10.67 in. at , Tes., 6.74 in. Coolness in parts of the West has prevailed during most nt Green B:LY,Wis., and 12.26 in. at Norfolk, Va. of 1964. By the end of September subnormal tempera- Much of the heavy precipitation was associated with tures had persisted for seven consecutive months at irontal activity. Heavy showers and thundershowers Pendleton, Oreg., Walln Walla, Wash., and Sail Diego, were set off in Iowa and Minnesota around the 10th by Calif.; eight months at Iialispell, Motit.; and ten months an active cold front which caused more showers in Tesas at Yuma, Ark.

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REFERENCES 2. E. NI. Ballenzweig, “Relation of Long-Period Circulation 1. J. Kamias, “Long Range Factors Affecting the Genesis and Paths Anoinali es to Tropical Stor 111 Format ion and Bloti on, ” of Tropical Cyclones,” Proceedinys 01 the UNESCO Sym- Journal of Meteorology, vol. 16, KO.2, Apr. 1959, pp. 121-139. posilLni on Typhoons, Tokyo, 0-12 A’ovember 1954, 1955, 3. U. S. Wcathcr Bureau, Weekly ll’eather and Crop Bullatin, PI). 213-219. National Sz~inmary,vol. L1, So. 40, Oct. 5, l!)(i4.

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