RotatingRotating Storms:Storms: SupercellsSupercells,, Tornadoes,Tornadoes, andand TropicalTropical StormsStorms

AT 351 Lab 12 April 14, 2008

SupercellsSupercells

! Characterized by rotating updrafts (called a mesocyclone) ! Differ from multicell cluster because smaller updrafts merge into a main rotated updraft rather than developing separate and competing cells ! Can persist for 12 hours and travel hundreds of miles ! Forms in environments of strong winds aloft ! Winds veer with height from the surface ! Can be classified as either High Precipitation (HP) or Low Precipitation (LP) SupercellSupercell

HPHP SupercellsSupercells

•Dark rain and hail core •Prolific producers of lightning and flash floods LPLP SupercellsSupercells

! Typically associated with a dry line ! Typically small and lacking in rainfall

TornadoesTornadoes

! Formation ! Life Cycle ! Definition ! Types ! Damage ! EF-scale FormationFormation

! We know relatively little about the formation of tornadoes, known as tornadogenesis ! However, we do know the basic steps along the way ! It is the details we are missing, but they are very crucial details

VorticityVorticity

! Vorticity is the name we give to a natural spin in the air ! Caused mainly by ! Just like a pinwheel Non-SupercellNon-Supercell TornadoTornado FormationFormation ! Vertical wind shear crucial

VorticityVorticity TiltingTilting

! After horizontal rotation is established, the storm’s updraft works to tilt it upright ! Now the storm has a vertically rotating component SuctionSuction VorticesVortices

! Many violent tornadoes contain smaller whirls that rotate inside them ! Rotate faster, and do a great deal of damage ! How these form is still not completely understood

SupercellSupercell TornadoTornado FormationFormation

! Remember: supercell is a long lived storm ! Contains a rotating updraft ! Rotating updraft can contribute to the , as well as vertical wind shear ! How does this rotating updraft form ! Examine the winds at different heights SupercellSupercell TornadoTornado FormationFormation

! Can also get vertical wind shear at surface, that adds or forms this rotation

SupercellSupercell TornadoTornado FormationFormation SupercellSupercell TornadoTornado FormationFormation

! Why rear part of storm ! SW winds aloft usually blow precipitation NE ! Also, mesocyclone can circulate precipitation counter- clockwise

StrongerStronger UpdraftUpdraft

! As the storm matures, its updraft will strengthen ! The updraft creates a low pressure center under the storm ! The new pressure center begins to draw in air from around the storm ! This inflow includes cold air from the downdraft that cannot get away WallWall CloudCloud

! Since some of the air being drawn in is colder than the rest of the storm, it will reach saturation and condense sooner on its way up ! Since it condenses lower, it makes the appear to be descending ! This is called a ! The sighting of a wall cloud will prompt a tornado warning

FunnelFunnel CloudCloud

! The storm’s downdraft does two things ! Pushes the rotating column to the ground ! In stretching it, makes the rotation stronger ! As the rotating air descends, it forms the familiar funnel shape we all know and love GroundGround ContactContact

! Once the rotation reaches the ground, the downward moving air will spread out ! Some will go back toward the center of the funnel, converging and forcing it back up ! The upward motion will begin to kick up debris ! At this point, the rotation has made a complete column to the ground and is officially called a tornado DissipationDissipation

! At this point, the downdraft that brought the rotation to the ground to begin with is wrapped around the tornado ! (RFD for short) ! Cuts off warm inflow, thus killing the very tornado it created ! Causes funnel to thin out into a ropelike shape Ingredients to Make a Stronger Tornado ! The same things that make will cause tornadoes to be stronger ! More wind shear creates longer lasting rotation ! High CAPE gives the storm plenty of energy ! Warm, moist air gives the tornado plenty of fuel to last longer and grow stronger DamageDamage

! The highest winds on Earth are found inside tornadoes ! The strongest tornado ever recorded had winds over double that of the strongest hurricane ! Damage can be beyond devastation

FujitaFujita ScaleScale

! In 1973, Ted Fujita of the Univ. of devised a scale for rating the intensity of a tornado ! Subjective damage scale that classified a tornado on a scale from F0 to F5 ! F5 is the highest – don’t listen to anyone that says anything different ! Assessed by going to damage sites and using a checklist EnhancedEnhanced FujitaFujita ScaleScale

! Proposed in early 2005, adopted in 2007 ! Replaces ! Uses more criteria to assess damage ! Has 28 “damage indicators” that surveyors look at

OPERATIONAL EF FUJITA SCALE DERIVED EF SCALE SCALE

F Fastest 1/4- 3 Second Gust EF 3 Second EF 3 Second Number mile (mph) (mph) Number Gust (mph) Number Gust (mph)

0 40-72 45-78 0 65-85 0 65-85 1 73-112 79-117 1 86-109 1 86-110 2 113-157 118-161 2 110-137 2 111-135 3 158-207 162-209 3 138-167 3 136-165 4 208-260 210-261 4 168-199 4 166-200 5 261-318 262-317 5 200-234 5 Over 200

http://www.spc.noaa.gov/efscale/ef-scale.html EF0EF0

“Light damage” ! Tree branches broken ! Chimney damage ! Sign damage

EF1EF1

! “Moderate Damage” ! Roof damage ! Windows broken ! Mobile homes damaged or overturned EF2EF2

! “Considerable damage” ! Good houses lose roof ! Cars lifted off ground ! Mobile homes destroyed

EF3EF3

! “Severe damage” ! Houses lose entire stories ! Trains overturned ! Bark ripped from trees ! Heavy cars thrown EF4EF4

! “Devastating damage” ! Well built houses leveled ! Cars ---> missiles

EF5EF5

! “Incredible damage” ! Only one happened this year (Greensburg, KS) ! Strong frame houses obliterated and scattered over county ! Cars thrown over 100m AA FewFew FactsFacts

! The EF scale is not a wind scale; the wind speeds are merely a benchmark ! The last F5 happened in 1999, and before that in 1998 (actually 2, eight days apart) ! There were 53 official F5’s from 1950 to 2006 ! And now one EF5

TheThe 0303 MayMay 19991999 TornadoTornado

! Hit Bridge Creek and Moore, OK in the evening (around 19:00 CDT) ! Moved through southern Oklahoma City ! Killed 36 people ! Contained strongest winds ever recorded on Earth ! 318 mph, measured by Joshua Wurman and the Doppler on Wheels DamageDamage inin MooreMoore

! Homes completely removed from foundations, leaving only a slab of concrete ! Asphalt pulled off of Interstate 35, leaving only dirt behind ! Trucks lofted high enough to be picked up on radar, then wrapped all the way around telephone poles

0404 MayMay 20072007 TornadoTornado

! Destroyed Greensburg, KS in the night ! Hit at 21:40, square on ! Demolished 95% of buildings in the town ! 10 deaths ! Entire town evacuated afterward ! Responsible for 4th “Tornado Emergency” ever declared TropicalTropical StormsStorms What is required for TS formation?

! Warm and moist air ! A really good reason why they form over tropical oceans – lots of latent heat! ! Typically tropical storms only form over areas of the ocean with a temperature higher than 26°C ! Rotation ! Comes from coriolis force ! Tropical storms form near, but not on, the equator ! Continued fuel ! A tropical storm can strengthen if it continues to move over warm water, and will weaken once it hits dry land ! NO (or very weak) vertical wind shear ! Unlike storms in the mid-latitudes which need shear to organize, tropical storms will be sheared apart and prevented from organizing

StagesStages ofof developmentdevelopment

! Tropical disturbance (tropical wave) ! Formation of group of thunderstorms, typically in association with an easterly wave ! Tropical depression ! When winds exceed 20 knots ! Beginning of formation of closed low pressure center ! Appear on satellite as cluster of thunderstorms ! Will be assigned a number (e.g. “tropical depression one”) StagesStages ofof developmentdevelopment ! Tropical Storm ! Winds exceed 35 knots ! Central pressure drops ! On satellite, more organized, circular shape observed ! Storm gets a name ! Hurricane ! Sustained winds exceed 64 knots ! Surface pressure continues to drop ! On satellite imagery, well- defined cyclonic rotation around the central circulation, with observation of

StagesStages ofof DevelopmentDevelopment DissipationDissipation

! Weaken rapidly when move over colder water ! Lose heat source ! Dissipate rapidly when move over land ! Lose energy source ! Winds decrease in strength (due to added friction) and blow more directly into center, causing central pressure to rise ! May cause flooding as continues to move over land

StructureStructure ofof aa HurricaneHurricane

! Surface: ! Inflow of moist, tropical air, rises, condenses, releases latent heat ! Rising motion creates center of low pressure ! Produces a cyclonic circulation ! Aloft: ! Air diverges, producing an anticyclonic circulation ! As outflow reaches periphery of storm, begins to sink and warm, creating clear skies TheThe eyeeye

! Coriolis deflects converging wind around the center ! Vigorous convection in the eye wall warms the air due to release of latent heat ! Produces slightly higher pressures aloft, initiating downward motion within the center ! Eye characterized by warm air (due to compression), clear skies (sinking motion), and low wind speeds

StormStorm SurgeSurge

! Storm surge has historically brought 90% of the death and destruction during hurricanes, and is the primary reason that coastal areas are evacuated as storms approach. ! Winds push water onshore – can add to normal tides and create waves over 10 ft high ! Strongest where storm motion and winds are in the same direction (on the right side of the storm) ! Gradually sloped coastlines are inundated by surge waters moving onshore, though steeper coastlines will cause breaking waves SaffirSaffir-Simpson-Simpson ScaleScale

Maximum sustained wind Minimum surface Storm Saffir- speed pressure surge Simpson Category mph m/s kt mb ft m

1.0- 1 74-95 33-42 64-82 greater than 980 3-5 1.7 1.8- 2 96-110 43-49 83-95 979-965 6-8 2.6 9- 2.7- 3 111-130 50-58 96-113 964-945 12 3.8 13- 3.9- 4 131-155 59-69 114-135 944-920 18 5.6

5 156+ 70+ 136+ less than 920 19+ 5.7+

2007 2008 2009 2010 2011 2012 Andrea Arthur Ana Alex Arlene Alberto Barry Bertha Bill Bonnie Bret Beryl Chantal Cristobal Claudette Colin Cindy Chris Dean Dolly Danny Danielle Don Debby Erin Edouard Erika Earl Emily Ernesto Felix Fay Fred Fiona Franklin Florence Gabrielle Gustav Grace Gaston Gert Gordon Humberto Hanna Henri Hermine Harvey Helene Ingrid Ike Ida Igor Irene Isaac Jerry Josephine Joaquin Julia Jose Joyce Karen Kyle Kate Karl Katia Kirk Lorenzo Laura Larry Lisa Lee Leslie Melissa Marco Mindy Matthew Maria Michael Noel Nana Nicholas Nicole Nate Nadine Olga Omar Odette Otto Ophelia Oscar Pablo Paloma Peter Paula Philippe Patty Rebekah Rene Rose Richard Rina Rafael Sebastien Sally Sam Shary Sean Sandy Tanya Teddy Teresa Tomas Tammy Tony Van Vicky Victor Virginie Vince Valerie Wendy Wilfred Wanda Walter Whitney William 2020 CostliestCostliest USUS HurricanesHurricanes Rank Name Year Category Damage (U.S.)* 1. Katrina (LA/MS/AL/SE FL) 2005 3 $75,000,000,000 2. Andrew (SE FL/SE LA) 1992 5 $34,954,825,000 3. Charley (FL) 2004 4 $14,000,000,000 4. Ivan (FL/AL) 2004 3 $13,000,000,000 5. Wilma (FL) 2005 3 $12,200,000,000 6. Rita (LA/TX) 2005 3 $10,000,000,000 7. Hugo (SC) 1989 4 $9,739,820,675 8. Frances (FL) 2004 2 $8,860,000,000 9. Agnes (NE U.S.) 1972 1 $8,602,500,000 10. Betsy (FL/LA) 1965 3 $8,516,866,023 11. Jeanne (FL) 2004 3 $6,500,000,000 12. Camille (MS/AL) 1969 5 $6,992,441,549 13. Georges (PR/MS) 1998 5 $6,300,000,000 14. Allison (TX/LA) 2001 T.S. $5,000,000,000 15. Diane (NE U.S.) 1955 1 $5,540,676,187 16. Frederic (AL/MS) 1979 3 $4,965,327,332 17. New England 1938 3 $4,748,580,000 18. Floyd (NC) 1999 4 $4,666,817,360 19. Fran (NC) 1996 3 $3,670,400,000 20. Opal (NW FL/AL) 1995 3 $3,520,596,085

2020 DeadliestDeadliest USUS HurricanesHurricanes Rank Name Year Category Deaths 1. Great Galveston Hurricane (TX) 1900 4 8000 2. FL (Lake Okeechobee) 1928 4 2500 3. Katrina (LA/MS/FL/GA/AL) 2005 3 1350 4. Cheniere Caminanda (LA) 1893 4 1100-1400 5. Sea Islands (SC/GA) 1893 3 1000-2000 6. GA/SC 1881 2 700 7. Great Labor Day Hurricane (FL Keys) 1935 5 408 8. Last Island (LA) 1856 4 400 9. Audrey (SW LA/N TX) 1957 4 390 10. LA (Grand Isle) 1909 4 350 10. Miami Hurricane (FL/MS/AL/Pensacola) 1926 4 372 12. FL (Keys)/S. TX 1919 4 287# 13. LA (New Orleans) 1915 4 275 13. TX (Galveston) 1915 4 275 15. Camille (MS/LA) 1969 5 256 15. New England 1938 3* 256 17. Diane (NE U.S.) 1955 1 184 18. GA, SC, NC 1898 4 179 19. TX 1875 3 176 20. SE FL 1906 2 164 National Hurricane Center Forecast Parameters

! Track ! Tropical cyclone positions 0 to 120 hr ! Intensity ! Maximum wind 0 to 120 hr ! Typically harder to forecast than track ! Wind Structure ! Radii of 34, 50 kt winds 0 to 72 hr ! Radii of 64 kt winds 0 to 36 hr ! Watches ! Hurricane conditions possible in next ~36 hr ! Warning ! Hurricane conditions likely in next ~24 hr ! Probabilities of 34, 50 and 64 kt winds 0 to 120 hr

Courtesy Mark DeMaria

Hurricanes vs. Mid-latitude Storms

! Both are areas of surface low pressure, with winds moving counterclockwise at the surface in the NH ! Energy source ! Hurricane: warm water, latent heat of condensation ! Mid-lat: horizontal temperature contrasts ! Vertical structure ! Hurricane: warm-core, weakens with height, high pressure aloft ! Mid-lat: cold-core, intensify with height, upper-level low or trough aloft ! Center ! Hurricane: eye with sinking air, skies clear ! Mid-lat: rising air in center, skies cloudy ! Winds ! Hurricane: strongest at surface ! Mid-lat: strongest aloft