514
WTNT43 KNHC 302047
TCDAT3
TROPICAL STORM FIONA DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082010
500 PM EDT MON AUG 30 2010
EARLIER TODAY...ABOUT 30 DROPSONDES WERE RELEASED DURING A G-V
RESEARCH MISSION BEING CONDUCTED BY THE NATIONAL CENTER FOR
ATMOSPHERIC RESEARCH NEAR THE AREA OF LOW PRESSURE LOCATED ABOUT
800 MILES EAST OF THE LESSER ANTILLES. ONE OF THE DROPSONDES
MEASURED A SURFACE WIND OF 35 KT APPROXIMATELY 120 N MI TO THE
NORTHEAST OF THE ESTIMATED CENTER. THIS MEASUREMENT AGREES WITH AN
ASCAT PASS FROM 1208 UTC...WHICH SHOWED A SWATH OF 30-35 KT WINDS
IN THAT SAME AREA. CONVECTION HAS BEEN A LITTLE THIN FOR MOST OF
THE DAY...BUT BANDING FEATURES HAVE RECENTLY BECOME MORE PROMINENT
MAINLY OVER THE WESTERN SEMICIRCLE. GIVEN THE INCREASE IN
CONVECTION AND SINCE TROPICAL STORM FORCE WINDS ARE ALREADY
OCCURRING...THE SYSTEM IS BEING DIRECTLY UPGRADED TO TROPICAL STORM
FIONA.
SINCE FIONA STILL LACKS SOME ORGANIZATION AND THE WIND FIELD IS
SOMEWHAT LARGE...THE CYCLONE WILL LIKELY HAVE A DIFFICULT TIME
INTENSIFYING OVER THE NEXT DAY OR SO. I DO NOT BELIEVE THIS
STRUCTURE IS HANDLED WELL BY THE STATISTICAL INTENSITY
GUIDANCE...WHICH INTENSIFY FIONA TO A HURRICANE IN 36 TO 48
HOURS...SO I AM INCLINED TO LEAN CLOSER TO THE DYNAMICAL GFDL AND
HWRF AT THIS POINT. IN FACT...THE GFS DISSIPATES THE CYCLONE WITHIN
2 TO 3 DAYS. THE OFFICIAL FORECAST THEREFORE SHOWS MINIMAL
STRENGTHENING OVER THE NEXT 1 TO 2 DAYS AND THEN LEVELS OUT THE
INTENSITY FOR DAYS 3 THROUGH 5...WHEN IT APPEARS THAT INCREASING
VERTICAL SHEAR COULD BECOME A LIMITING FACTOR.
THE SURFACE CENTER HAS BEEN A LITTLE DIFFICULT TO LOCATE...AND THE
INITIAL MOTION IS AN UNCERTAIN 270/21. TRACK MODEL GUIDANCE IS IN
GOOD AGREEMENT FOR THE NEXT 48 HOURS AND SHOWS FIONA TURNING TOWARD
THE NORTHWEST...GENERALLY FOLLOWING EARL AROUND THE WESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE. AFTER THAT...THE
GFDL...HWRF...AND GFS KEEP FIONA AS A WEAK SYSTEM AND SHOW IT
CONTINUING TO THE NORTH IN THE LOW-LEVEL FLOW BEHIND EARL. THE
ECMWF...ON THE OTHER HAND...SHOWS A STRONGER FIONA AND SUGGESTS
THAT THE SUBTROPICAL RIDGE COULD BUILD BACK TO THE WEST BEFORE THE
CYCLONE CAN RECURVE. THE OFFICIAL FORECAST IS VERY CLOSE TO THE
MODEL CONSENSUS TVCN FOR THE FIRST 48 HOURS BUT THEN LIES A LITTLE
NORTH OF THE CONSENSUS IN FAVOR OF THE TRACKS OF THE WEAKER GFDL
AND HWRF.
FORECAST POSITIONS AND MAX WINDS
INITIAL 30/2100Z 14.4N 48.7W 35 KT
12HR VT 31/0600Z 14.9N 51.9W 35 KT
24HR VT 31/1800Z 15.8N 55.9W 40 KT
36HR VT 01/0600Z 17.2N 59.2W 45 KT
48HR VT 01/1800Z 19.3N 62.0W 45 KT
72HR VT 02/1800Z 24.0N 66.0W 40 KT
96HR VT 03/1800Z 27.5N 68.0W 40 KT
120HR VT 04/1800Z 29.0N 69.0W 40 KT
$$
FORECASTER BERG
120
WTNT42 KNHC 302047
TCDAT2
HURRICANE EARL DISCUSSION NUMBER 22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072010
500 PM AST MON AUG 30 2010
THE RECONNAISSANCE AIRCRAFT MEASURED 116 KT FLIGHT-LEVEL WINDS AND
108 KT SFMR SURFACE WINDS SHORTLY AFTER 1500 UTC. THIS WAS THE
BASIS FOR THE EARLIER INCREASE IN INTENSITY. SINCE THAT TIME...THE
PRESSURE HAS CONTINUED TO DROP AND WAS DOWN TO 955 MB ON THE LAST
DROPSONDE RELEASED IN THE EYE AROUND 1700 UTC. SINCE THE AIRCRAFT
DEPARTED EARL...THE EYE HAS CONTINUED TO CLEAR AND IS SURROUNDED BY
CLOUD TOPS TO -70 DEGREES CELSIUS OR COLDER. OBJECTIVE SATELLITE
INTENSITY ESTIMATES HAVE INCREASED TO JUST ABOVE 6.0 ON THE DVORAK
SCALE AND SUPPORT AN INITIAL INTENSITY OF 115 KT...CATEGORY FOUR ON
THE SAFFIR-SIMPSON HURRICANE WIND SCALE.
EARL IS EXPECTED TO REMAIN IN A LOW SHEAR ENVIRONMENT AND OVER WARM
WATER DURING THE NEXT FEW DAYS AND SOME ADDITIONAL STRENGTHENING IS
LIKELY IN THE SHORT TERM. THEREAFTER...EYEWALL CYCLES WILL LIKELY
INDUCE SOME FLUCTUATIONS IN INTENSITY...WHICH ARE DIFFICULT TO
PREDICT. THE NHC FORECAST IS AGAIN NEAR THE HIGH END OF THE
INTENSITY GUIDANCE. AT DAYS 4 AND 5...THE HURRICANE IS FORECAST TO
MOVE OVER COOLER WATER AND INTO AN AREA OF INCREASING SHEAR WHICH
SHOULD RESULT IN WEAKENING.
THE INITIAL MOTION IS 290/13. THE FORECAST REASONING REMAINS
UNCHANGED AS EARL IS EXPECTED TO TURN NORTHWESTWARD IN ABOUT 24
HOURS AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. THE
TRACK GUIDANCE HAS SHIFTED NOTICEABLY WESTWARD DURING THE FIRST
48 HOURS...WITH THE GFS AND ECMWF ON THE EASTERN EDGE OF THE
ENVELOPE. THE OFFICIAL FORECAST HAS BEEN ADJUSTED WESTWARD...
PRIMARILY THROUGH 72 HOURS...AND LIES BETWEEN THE GFS/ECMWF AND THE
MULTI-MODEL CONSENSUS.
THIS IS A GOOD TIME TO REMIND EVERYONE THAT NHC AVERAGE TRACK
FORECAST ERRORS ARE 200 TO 300 MILES AT DAYS 4 AND 5. GIVEN THIS
UNCERTAINTY...IT IS TOO SOON TO DETERMINE WHAT PORTION OF THE U.S.
EAST COAST MIGHT SEE DIRECT IMPACTS FROM EARL.
FORECAST POSITIONS AND MAX WINDS
INITIAL 30/2100Z 19.3N 64.7W 115 KT
12HR VT 31/0600Z 20.2N 66.3W 125 KT
24HR VT 31/1800Z 21.7N 68.1W 130 KT
36HR VT 01/0600Z 23.4N 70.1W 130 KT
48HR VT 01/1800Z 25.8N 72.1W 125 KT
72HR VT 02/1800Z 31.6N 74.7W 115 KT
96HR VT 03/1800Z 38.0N 71.0W 95 KT
120HR VT 04/1800Z 45.5N 63.0W 70 KT...INLAND
$$
FORECASTER BROWN
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