TROPICAL STORM COLIN dissussions

[NHC Olney Maryland]

Tropical depression 4/Topical storm colin will be posted here

[NHC Olney Maryland]

TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL/OLNEY MD AL042010
1100 AM EDT MON AUG 02 2010

DATA FROM AN 1148 UTC ASCAT PASS SUGGEST THAT THE DISTURBANCE IN THE
TROPICAL ATLANTIC NOW HAS A WELL-DEFINED SURFACE CIRCULATION...AND
ADVISORIES ARE INITIATED ON TROPICAL DEPRESSION FOUR. THE INITIAL
INTENSITY IS SET AT 30 KT IN AGREEMENT WITH THE ASCAT DATA AND
DVORAK DATA T-NUMBERS OF 2.0 FROM TAFB AND SAB.

THE LOW-LEVEL CENTER APPEARS TO BE LOCATED ON THE SOUTHEASTERN EDGE
OF THE DEEP CONVECTION...AND IS MOVING RATHER BRISKLY TOWARD THE
WEST-NORTHWEST AT ABOUT 15 KT. MUCH OF THE GUIDANCE SUGGESTS AN
EVEN FASTER MOTION IS LIKELY DURING THE NEXT COUPLE OF DAYS AS THE
DEPRESSION IS STEERED BY A STRONG SUBTROPICAL RIDGE TO ITS NORTH.
IN FOUR OR FIVE DAYS...THE GLOBAL MODELS SHOW A WEAKNESS DEVELOPING
IN THE RIDGE...WHICH SHOULD RESULT IN A TURN TOWARD THE NORTHWEST
WITH A DECREASE IN FORWARD SPEED. THERE IS QUITE A BIT OF SPREAD
IN THE MODELS BY THE END OF THE PERIOD...WITH THE GFS ON THE LEFT
SIDE OF THE GUIDANCE SUITE AND THE HWRF AND ECMWF FARTHER RIGHT
SHOWING MORE RECURVATURE. THE OFFICIAL FORECAST IS CLOSE TO THE
MULTI-MODEL TVCN CONSENSUS AND IN BEST AGREEMENT WITH THE GFDL. IT
IS WORTH REMINDING USERS THAT THE AVERAGE ERROR OF THE OFFICIAL
TRACK FORECAST AT DAYS 4 AND 5 IS 250 TO 300 MILES.

THE ENVIRONMENT APPEARS FAVORABLE FOR SOME STRENGTHENING OVER THE
NEXT COUPLE OF DAYS...BUT AFTER THAT TIME VERTICAL WIND SHEAR IS
EXPECTED TO INCREASE AS THE CYCLONE APPROACHES AN UPPER-LEVEL
TROUGH AROUND 65W. THE SHIPS MODEL SHOWS THE SHEAR INCREASING TO
AROUND 30 KT BY 72 HOURS...AND THE OFFICIAL FORECAST SHOWS A PEAK
IN INTENSITY AROUND THAT TIME...IN BEST AGREEMENT WITH THE ICON
INTENSITY CONSENSUS. IF THE CYCLONE DOES NOT INTENSIFY IN THE NEXT
DAY OR SO...IT COULD STRUGGLE TO MAINTAIN A CLOSED SURFACE
CIRCULATION WITH SUCH A FAST FORWARD SPEED...AND COULD OPEN BACK UP
INTO A TROPICAL WAVE.

FORECAST POSITIONS AND MAX WINDS

INITIAL 02/1500Z 12.6N 41.1W 30 KT
12HR VT 03/0000Z 13.5N 44.0W 35 KT
24HR VT 03/1200Z 14.8N 48.9W 40 KT
36HR VT 04/0000Z 16.4N 53.4W 45 KT
48HR VT 04/1200Z 18.4N 57.4W 50 KT
72HR VT 05/1200Z 22.0N 63.0W 50 KT
96HR VT 06/1200Z 26.0N 66.5W 45 KT
120HR VT 07/1200Z 29.0N 68.5W 45 KT


FORECASTER MILLER/BURRUS

[NHC Olney Maryland]

TROPICAL STORM COLIN DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042010
500 AM EDT TUE AUG 03 2010

THE TROPICAL CYCLONE HAS BECOME BETTER ORGANIZED OVER THE PAST
SEVERAL HOURS. ENHANCED INFRARED SATELLITE IMAGES SHOW A CURVED
BAND WRAPPING HALFWAY AROUND THE CIRCULATION OVER THE WESTERN
SEMICIRCLE. DVORAK DATA T-NUMBERS ARE 2.5 FROM BOTH TAFB AND SAB
SUPPORTING A CURRENT INTENSITY ESTIMATE OF 35 KT. THEREFORE THE
SYSTEM IS BEING NAMED AT THIS TIME. COLIN IS EXPECTED TO BE IN AN
ENVIRONMENT CONDUCIVE FOR SOME STRENGTHENING...WITH MODERATE TO
WEAK VERTICAL SHEAR AND ANTICYCLONIC UPPER-LEVEL FLOW...FOR THE
NEXT 36 HOURS OR SO. THEREAFTER...INCREASING WESTERLY SHEAR
ASSOCIATED WITH AN UPPER-LEVEL LOW OVER THE SOUTHWESTERN NORTH
ATLANTIC SHOULD BEGIN TO IMPACT THE STORM. THE OFFICIAL FORECAST
CALLS FOR MODEST STRENGTHENING DURING THE NEXT 36 HOURS FOLLOWED BY
A LEVELING OFF OF INTENSITY THEREAFTER. THIS IS SIMILAR TO THE
LATEST GFDL MODEL FORECAST AND NOT TOO DISSIMILAR TO THE PREVIOUS
NHC FORECAST. NONE OF THE DYNAMICAL OR STATISTICAL/DYNAMICAL
INTENSITY GUIDANCE BRINGS COLIN TO HURRICANE STRENGTH OVER THE NEXT
5 DAYS.

CENTER FIXES SHOW THAT THE STORM CONTINUES TO MOVE BRISKLY TOWARD
THE WEST-NORTHWEST...AND THE INITIAL MOTION ESTIMATE REMAINS AT
285/20. AT THIS TIME...THE STEERING FOR COLIN IS BEING PROVIDED DUE
TO A SUBTROPICAL RIDGE TO THE NORTH AND A LOW- TO MID-TROPOSPHERIC
EASTERLY JET. THIS RELATIVELY FAST STEERING CURRENT SHOULD MORE OR
LESS PREVAIL FOR THE NEXT COUPLE OF DAY OR SO. THEREAFTER...THE
TROPICAL CYCLONE IS LIKELY TO APPROACH A WEAKNESS IN THE
SUBTROPICAL RIDGE. THIS WOULD CAUSE A GRADUAL TURN TO THE RIGHT
ALONG WITH A DECREASING FORWARD SPEED. THE TRACK GUIDANCE MODELS
ARE IN FAIRLY GOOD AGREEMENT OVER THE NEXT 36 HOURS. AFTER THAT
FORECAST TIME...THE MODELS BECOME MODERATELY DIVERGENT WITH THE GFS
AND ECMWF ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE AND THE GFDL
AND HWRF ON THE RIGHT. THE OFFICIAL TRACK FORECAST IS ROUGHLY IN
THE MIDDLE OF THE ENVELOPE...FAIRLY CLOSE TO THE DYNAMICAL MODEL
CONSENSUS...AND VERY CLOSE TO THE PREVIOUS NHC FORECAST.

OBSERVATIONS FROM NOAA DATA BUOY 41041 OVER THE CENTRAL TROPICAL
ATLANTIC INDICATE THAT COLIN IS A SMALL TROPICAL STORM...AND THE
WIND RADII SHOWN IN THE ADVISORY MIGHT BE GENEROUS.

INTERESTS IN THE NORTHERN LEEWARD ISLANDS SHOULD FOLLOW THE PROGRESS
OF COLIN. AT THIS TIME...BASED ON THE FORECAST TRACK...WIND
FIELD...AND REASONABLE UNCERTAINTIES...NO TROPICAL STORM WATCHES OR
WARNINGS ARE REQUIRED.

FORECAST POSITIONS AND MAX WINDS

INITIAL 03/0900Z 14.0N 47.2W 35 KT
12HR VT 03/1800Z 15.1N 50.3W 40 KT
24HR VT 04/0600Z 16.8N 54.5W 45 KT
36HR VT 04/1800Z 18.6N 58.3W 50 KT
48HR VT 05/0600Z 20.6N 61.5W 50 KT
72HR VT 06/0600Z 24.5N 66.5W 50 KT
96HR VT 07/0600Z 28.0N 68.5W 50 KT
120HR VT 08/0600Z 31.0N 69.5W 50 KT


FORECASTER BURRUS

[NHC Olney Maryland]

TROPICAL STORM COLIN DISCUSSION NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL/OLNEY MD AL042010
500 PM EDT TUE AUG 03 2010

THE CENTER OF COLIN PASSED NEAR OR OVER THE WOODS HOLE NTAS BUOY
ABOUT 15Z...WHICH REPORTED A MINIMUM PRESSURE OF 1007 MB AND A
SMALL LOW PRESSURE CENTER. HOWEVER...NEITHER THAT BUOY NOR THE
NEARBY NOAA BUOY 41040 REPORTED WINDS SUPPORTING A CLOSED
CIRCULATION...AND WESTERLY WINDS ARE NOT CURRENTLY APPARENT IN LOW
CLOUD MOTIONS SOUTH OF THE CENTER. ADDITIONALLY...THE ASSOCIATED
CONVECTION HAS BECOME VERY DISORGANIZED. BASED ON THIS...COLIN HAS
DEGENERATED INTO A REMNANT LOW WITH GALE-FORCE WINDS OVER A SMALL
AREA NORTH OF THE CENTER.

IN THE SHORT TERM...REGENERATION APPEARS UNLIKELY AS THE REMNANTS OF
COLIN ENCOUNTER WESTERLY VERTICAL SHEAR CAUSED BY THE STRONG
LOW-LEVEL FLOW AND WESTERLY WINDS ASSOCIATED WITH A COMPLEX
UPPER-LEVEL TROUGH OVER THE SOUTHWESTERN ATLANTIC. HOWEVER...NONE
OF THE DYNAMICAL MODELS FORECAST THE REMNANTS OF COLIN TO DISSIPATE
DURING THE FORECAST PERIOD...AND THEY FORECAST THAT THE SYSTEM
COULD REACH A MORE FAVORABLE ENVIRONMENT OFF THE SOUTHEASTERN COAST
OF THE UNITED STATES BY DAY 5. BASED ON THIS...THE INTENSITY
FORECAST CALLS FOR THE REMNANTS OF COLIN TO DROP BELOW GALE FORCE
DURING THE NEXT 12 HR AND CONTINUE AS A 30 KT REMNANT LOW THROUGH
96 HR. AFTER THAT...THE DISTURBANCE COULD REGENERATE INTO A
TROPICAL CYCLONE AS SHOWN IN THE 120-HR FORECAST.

THE INITIAL MOTION IS AN EXTREMELY RAPID 285/30. ALL GUIDANCE
AGREES THAT THE REMNANTS OF COLIN SHOULD CONTINUE WEST-
NORTHWESTWARD FOR THE NEXT 48-72 HR WITH A SIGNIFICANT DECREASE IN
FORWARD SPEED. THE NEW FORECAST TRACK IS SIMILAR IN DIRECTION TO
THE PREVIOUS FORECAST...BUT IS MUCH FASTER. AFTER THAT TIME...THE
SYSTEM SHOULD TURN NORTHWESTWARD INTO A BREAK IN THE SUBTROPICAL
RIDGE NEAR THE EASTERN COAST OF THE UNITED STATES. MOST OF THE
DYNAMICAL MODELS HAVE SHIFTED THEIR 96-120 HR FORECASTS WESTWARD...
AND THE OFFICIAL FORECAST WILL DO LIKEWISE.

INTERESTS IN THE NORTHERN LEEWARD ISLANDS AND THE VIRGIN ISLANDS
SHOULD FOLLOW THE PROGRESS OF THE REMNANTS OF COLIN.

THIS IS THE LAST ADVISORY ISSUED BY THE NATIONAL HURRICANE CENTER ON
THIS SYSTEM UNLESS REGENERATION OCCURS. ADDITIONAL INFORMATION ON
THIS SYSTEM CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE
NATIONAL WEATHER SERVICE...UNDER AWIPS HEADER NFDHSFAT1 AND WMO
HEADER FZNT01 KWBC.

FORECAST POSITIONS AND MAX WINDS

INITIAL 03/2100Z 15.8N 53.8W 35 KT...POST-TROP/REMNT LOW
12HR VT 04/0600Z 16.8N 57.2W 30 KT...POST-TROP/REMNT LOW
24HR VT 04/1800Z 18.4N 60.8W 30 KT...POST-TROP/REMNT LOW
36HR VT 05/0600Z 20.0N 63.8W 30 KT...POST-TROP/REMNT LOW
48HR VT 05/1800Z 21.7N 66.5W 30 KT...POST-TROP/REMNT LOW
72HR VT 06/1800Z 25.0N 70.0W 30 KT...POST-TROP/REMNT LOW
96HR VT 07/1800Z 28.0N 72.5W 30 KT...POST-TROP/REMNT LOW
120HR VT 08/1800Z 30.0N 73.5W 30 KT...TROPICAL DEPRESSION


FORECASTER BEVEN/ BURRUS