Tropical Storm Gabrielle Has Formed… Tropical Update Wednesday 9:40pm

Warnings_361

THE SATELLITE PRESENTATION OF THE CYCLONE CONSISTS OF A SMALL AREA OF VERY DEEP CONVECTION NEAR AND NORTHEAST OF THE SURFACE CENTER WHILE THE CONVECTIVE BANDS HAVE LARGELY DISSIPATED OVER THE PAST
FEW HOURS. THE LARGE-SCALE OUTFLOW PATTERN OVER THE CYCLONE IS EXCELLENT WITH AN ENHANCED POLEWARD OUTFLOW CHANNEL SEEN IN WATER VAPOR IMAGERY. BASED ON THE LATEST SATELLITE CLASSIFICATIONS FROM BOTH TAFB AND SAB…THE INITIAL INTENSITY IS SET TO 35 KT…AND THE DEPRESSION IS NOW TROPICAL STORM GABRIELLE.

DROPSONDE DATA FROM THE NASA GLOBAL HAWK AIRCRAFT SUGGEST THAT THE CIRCULATION OF GABRIELLE IS TILTED TO THE NORTHEAST WITH HEIGHT… WITH A MID-LEVEL CIRCULATION SEEN IN DATA FROM THE SAN JUAN WSR-88D RADAR. THIS TILTED STRUCTURE IS CONSISTENT WITH SOUTHERLY TO SOUTHWESTERLY VERTICAL SHEAR OF 5 TO 10 KT SHOWN OVER THE CYCLONE BY THE UW-CIMSS AND SHIPS MODEL ANALYSES. IN ADDITION…THE DROPSONDE DATA SHOWED DRY AIR IN THE MID LEVELS OF THE ATMOSPHERE AROUND GABRIELLE. GIVEN THE ENVIRONMENT…THE SOMEWHAT DISORGANIZED
STATE OF THE CIRCULATION…POSSIBLE LAND INTERACTION…AND THE PRESENCE OF THE LARGE AREA OF DISTURBED WEATHER NORTHEAST OF GABRIELLE…NOT MUCH STRENGTHENING IS EXPECTED IN THE SHORT TERM.
THE NHC FORECAST IS IN GOOD AGREEMENT WITH THE INTENSITY CONSENSUS AIDS FOR THE FIRST 24 HOURS. IT IS ENTIRELY POSSIBLE THAT THE LOW-LEVEL CIRCULATION WILL DISSIPATE IN THE NEXT 24 HOURS. ASSUMING THAT GABRIELLE SURVIVES…ONLY LIMITED INTENSIFICATION IS SHOWN LATER IN THE PERIOD AS THE SHEAR INCREASES DRAMATICALLY AHEAD OF AN UPPER-LEVEL TROUGH. THE NHC FORECAST REMAINS BELOW MUCH OF THE
INTENSITY GUIDANCE LATE IN THE PERIOD…WHICH SEEMS TOO HIGH GIVEN THE INCREASE IN SHEAR. THE NHC FORECAST IS ALSO SUPPORTED BY THE GLOBAL MODELS…WHICH DO NOT SHOW MUCH INTENSIFICATION AFTER GABRIELLE MOVES NORTH OF THE CARIBBEAN SEA.

THE LOW-LEVEL CENTER HAS BEEN DIFFICULT TO LOCATE…BUT THE GLOBAL HAWK DROPSONDE DATA SUGGEST IT REMAINS SOUTHWEST OF THE MID-LEVEL CENTER SEEN IN RADAR IMAGERY. GIVEN THE DIFFICULTY LOCATING THE
CENTER…THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 320/7. THE SYNOPTIC-SCALE TRACK REASONING HAS NOT CHANGED…AS GABRIELLE IS EXPECTED TO MOVE GENERALLY NORTHWESTWARD DURING THE NEXT DAY OR SO…FOLLOWED A TURN TOWARD THE NORTH BY 72 HOURS AS THE CYCLONE MOVES AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. LATE IN THE PERIOD AN ACCELERATION TOWARD THE NORTHEAST IS EXPECTED AHEAD OF AN UPPER-LEVEL TROUGH OVER THE WESTERN ATLANTIC. THE NHC TRACK FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS ONE THROUGH 72 HOURS AND LIES A LITTLE TO THE RIGHT OF MOST OF THE MODEL GUIDANCE DURING THIS PERIOD. AT DAYS 4 AND 5 THE NHC FORECAST IS A LITTLE TO THE RIGHT OF THE PREVIOUS ONE AND IS CLOSE TO THE GFS ENSEMBLE MEAN AND FSU SUPERENSEMBLE.

REGARDLESS OF THE EXACT TRACK OF THE CENTER OF GABRIELLE DURING THE NEXT 24 HOURS…THE MAIN THREAT WILL BE HEAVY RAINFALL OVER PORTIONS OF PUERTO RICO AND THE DOMINICAN REPUBLIC.

WVUA Chief Meteorologist Richard Scott

rscott@wvuatv.com

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Dry Days Continue… Tropical Depression 7 Forms… Wednesday Forecast Update – 4:15pm

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Good Wednesday afternoon to you! The weather felt great this morning, but temperatures quickly reached the hot range this afternoon. Most areas are in the 89 to 93 degree range, but humidity is low. Dewpoints across Alabama are in the upper 50s to lower 60s. Since the air is dry, there is no risk of rain this afternoon or tonight. Dry air heats and cools quickly, so temperatures will fall fast after sunset. Expect temperatures in the middle 80s at 7pm, middle 70s at 10pm and upper 60s after midnight. Expect clear skies overnight, with a calm wind.

Much of the week will feature dry air and similar weather. Daytime temperatures will top out in the lower 90s, with lows in the upper 60s. I don’t expect any rain around here through Sunday, as humidity remains low. A light north breeze will continue to pump drier air into Alabama, so no major changes are expected.

The north flow will end on Monday and Tuesday, so humidity will quickly stream back into the area. Highs will remain in the lower 90s, and a few afternoon storms are possible Monday through Wednesday. Expect lows in the lower 70s at night late in the weekend and early next week.

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Here’s a look at Tropical Depression 7 at this hour. The system will likely become a tropical storm at any time this evening or tonight. The path from the National Hurricane Center takes the storm near Puerto Rico and Hispaniola tomorrow afternoon. After the brush with the islands, the storm will turn north and then northeast over the weekend. Most computer models agree with this path, as a large upper air trough sets up along the east coast of the US. While it is likely TD 7 becomes a tropical storm, the chance of it becoming a hurricane is fairly low. If it does become a hurricane, it will be the first of the 2013 season… The rest of the Atlantic basin is fairly quiet.

Football Weather….

Alabama is off this weekend….

Auburn is taking on Arkansas State on Saturday in Auburn. If you’re going to the game, expect temperatures in the middle 80s at the 6:30pm kickoff. There is a low chance of a passing storm during the game. Temperatures will fall into the lower 80s at the end of the game.

Send us your weather pictures! Send them to weather@wvuatv.com. Also, look us up on facebook and twitter. Like us on facebook by searching facebook.com/wvuaweather or WVUA-TV Weather. You can find us on twitter by searching weather@wvuatv.comor WVUA-TV Weather. Great way to get weather updates! Plus, facebook is a great way to send us weather pictures. Simply tag us!

Join us live on WVUA-TV weekdays at 4, 5, 6 and 10 pm and weekends at 10pm for the very latest on your news, weather and sports.

Richard Scott
WVUA Chief Meteorologist
rscott@wvuatv.com
Twitter: Richard_wvua

 

Tropical Depression # 7 Forms…. Wednesday Update – 4pm

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Good Wednesday afternoon! It’s official… Tropical Depression 7 has formed in the northeast Caribbean. The center of circulation is about 100 miles south of Puerto Rico. Most computer models re-curve the storm into the open waters of the Atlantic in a few days, with no US impacts. Since there will be a trough across the east coast, I don’t expect a US landfall… Here’s the discussion and update from the National Hurricane Center:

TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013
500 PM AST WED SEP 04 2013

AIRCRAFT AND SATELLITE DATA FROM THIS AFTERNOON INDICATE THAT THE LOW PRESSURE SYSTEM SOUTH OF PUERTO RICO HAS JUST ENOUGH OF A CIRCULATION AND ORGANIZED CONVECTION TO BE CONSIDERED A TROPICAL
DEPRESSION. THE INITIAL INTENSITY IS SET TO 30 KT BASED ON A 41 KT FLIGHT-LEVEL WIND FROM THE AIR FORCE PLANE.

THE ENVIRONMENT NEAR THE DEPRESSION APPEARS TO BE CONDUCIVE FOR STRENGTHENING DURING THE NEXT DAY OR SO WHILE IT REMAINS FAR ENOUGH AWAY FROM HISPANIOLA. ONLY GRADUAL INTENSIFICATION IS FORECAST DUE TO THE SOMEWHAT DISORGANIZED INITIAL STATE OF THE DEPRESSION. AFTER THAT TIME…A COMBINATION OF INCREASING VERTICAL WIND SHEAR AND POSSIBLE LAND INTERACTION COULD SLOW THE DEVELOPMENT OF THE
CYCLONE. THE NHC FORECAST IS ON THE LOW SIDE OF THE GUIDANCE ENVELOPE…AND IS CLOSER TO THE SHIPS AND LGEM MODELS. THE WIND SPEED PREDICTION ALSO FITS THE GENERAL IDEA OF THE GLOBAL MODELS…WHICH SUGGEST THAT THE CYCLONE WILL STRUGGLE AFTER IT LEAVES THE CARIBBEAN SEA. SOME INTENSIFICATION…PERHAPS DUE TO BAROCLINIC PROCESSES…IS POSSIBLE AT LONG RANGE AS THE CYCLONE INTERACTS WITH A MID-LATITUDE TROUGH.

THE DEPRESSION APPEARS TO BE MOVING ROUGHLY 305/8 AROUND THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE OVER THE CENTRAL ATLANTIC OCEAN. A LARGE TROUGH OVER THE WESTERN ATLANTIC OCEAN IS EXPECTED TO CAUSE THE RIDGE TO BREAK ALONG ABOUT 70W…WHICH SHOULD CAUSE THE CYCLONE TO TURN NORTHWARD IN TWO OR THREE DAYS. ONE COMPLICATING FACTOR IS THE LARGER DISTURBANCE LOCATED A FEW HUNDRED MILES NORTHEAST OF THE DEPRESSION. THE INTERACTION OF THESE TWO FEATURES MAKES THIS TRACK FORECAST MORE UNCERTAIN THAN WOULD BE SUGGESTED BY THE OVERALL MODEL SPREAD. THE NHC FORECAST IS NOT TOO FAR FROM THE MODEL CONSENSUS EARLY ON…AND THEN IS A BIT SLOWER THAN THE CONSENSUS AFTER THAT TIME…PUTTING LESS WEIGHT ON THE NORTHWARD GFDL/HWRF SOLUTIONS.

Send us your weather pictures! Send them to weather@wvuatv.com. Also, look us up on facebook and twitter. Like us on facebook by searching facebook.com/wvuaweather or WVUA-TV Weather. You can find us on twitter by searching weather@wvuatv.comor WVUA-TV Weather. Great way to get weather updates! Plus, facebook is a great way to send us weather pictures. Simply tag us!

Join us live on WVUA-TV weekdays at 4, 5, 6 and 10 pm and weekends at 10pm for the very latest on your news, weather and sports.

Richard Scott
WVUA Chief Meteorologist
rscott@wvuatv.com
Twitter: Richard_wvua