Tropical Storm Erika Forms East of the Lesser Antilles - May Pose a Threat to the Area in Roughly a Week

000
WTNT31 KNHC 012047
TCPAT1
BULLETIN
TROPICAL STORM ERIKA ADVISORY NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
500 PM EDT TUE SEP 01 2009

...ERIKA FORMS EAST OF THE NORTHERN LEEWARD ISLANDS...TROPICAL
STORM WATCHES ISSUED...

AT 5 PM...2100 UTC...THE GOVERNMENT OF THE NETHERLANDS ANTILLES HAS
ISSUED A TROPICAL STORM WATCH FOR THE ISLAND OF ST. MAARTEN.

AT 5 PM...THE GOVERNMENT OF ANTIGUA AND BARBUDA HAS ISSUED A
TROPICAL STORM WATCH FOR THE ISLANDS OF ANTIGUA...BARBUDA...ST.
KITTS...NEVIS...AND ANGUILLA.

AT 5 PM...THE GOVERNMENT OF FRANCE HAS ISSUED A TROPICAL STORM WATCH
FOR THE ISLANDS OF ST. MARTIN AND ST. BARTHELEMY.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.

INTERESTS ELSEWHERE IN THE NORTHERN LEEWARD ISLANDS...U.S. AND
BRITISH VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE
PROGRESS OF ERIKA.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA
OUTSIDE OF THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR NATIONAL METEOROLOGICAL SERVICE.

AT 500 PM EDT...2100 UTC...THE CENTER OF TROPICAL STORM ERIKA WAS
LOCATED NEAR LATITUDE 17.2 NORTH...LONGITUDE 57.3 WEST OR ABOUT 390
MILES...625 KM...EAST OF THE NORTHERN LEEWARD ISLANDS.

ERIKA IS MOVING TOWARD THE WEST-NORTHWEST NEAR 9 MPH...15 KM/HR...
AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT COUPLE
OF DAYS. ON THIS TRACK THE CENTER OF ERIKA IS EXPECTED TO REMAIN
TO THE NORTHEAST OF THE LEEWARD ISLANDS.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/HR...WITH HIGHER
GUSTS. SOME SLOW STRENGTHENING IS FORECAST DURING THE NEXT COUPLE
OF DAYS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 105 MILES...165 KM
FROM THE CENTER.

THE LATEST MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RESERVE
RECONNAISSANCE AIRCRAFT IS 1007 MB...29.74 INCHES.

...SUMMARY OF 500 PM EDT INFORMATION...
LOCATION...17.2N 57.3W
MAXIMUM SUSTAINED WINDS...50 MPH
PRESENT MOVEMENT...WEST-NORTHWEST OR 300 DEGREES AT 9 MPH
MINIMUM CENTRAL PRESSURE...1007 MB

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 800 PM EDT FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 1100
PM EDT.

$$
FORECASTER BLAKE/FRANKLIN

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000
WTNT41 KNHC 012047
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062009
500 PM EDT TUE SEP 01 2009

AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT HAS BEEN INVESTIGATING
THE LOW PRESSURE AREA EAST OF THE LEEWARD ISLANDS AND HAS FOUND A
MINIMUM PRESSURE OF ABOUT 1007 MB AND A CLOSED...ALBEIT...BROAD
CIRCULATION. PEAK FLIGHT-LEVEL WINDS WERE 52 KT WITH SFMR DATA OF
ABOUT 45 KT. THUS...TROPICAL STORM ERIKA HAS FORMED WITH AN
INITIAL INTENSITY OF 45 KT.

SATELLITE IMAGES SHOW THAT ERIKA IS EXPERIENCING MODERATE
SOUTHWESTERLY SHEAR WITH THE CENTER NEAR THE WESTERN EDGE OF THE
DEEP CONVECTION. SOME STRENGTHENING OF THE STORM SEEMS POSSIBLE
DURING THE NEXT DAY OR TWO WHILE THE SSTS ARE WARM AND SHEAR
REMAINS MODERATE. HOWEVER...IN ABOUT TWO DAYS...GLOBAL MODELS
SIGNIFICANTLY INCREASE THE SHEAR NEAR THE TROPICAL CYCLONE AS
UPPER-LEVEL WESTERLIES FROM A MID-OCEANIC TROUGH OVER THE WESTERN
ATLANTIC IMPINGE ON THE SYSTEM. MOST OF THE GLOBAL MODELS SHOW
ERIKA WEAKENING AFTER TWO DAYS DUE TO THE SHEAR. THE TWO BIG
OUTLIERS IN THE MODEL GUIDANCE ARE THE GFDL/HWRF...WHICH FORM AN
ANTICYCLONE NEAR ERIKA AND MAKE IT A HURRICANE. THE NHC FORECAST
WILL SHOW SLOW INTENSIFICATION OVER THE FIRST COUPLE OF DAYS...THEN
WEAKENING THEREAFTER AS THE SHEAR TAKES OVER. THE NHC FORECAST WILL
BE CONSERVATIVE AT THIS TIME...BUT IT IS OF NOTE THAT ALMOST ALL OF
THE RELIABLE INTENSITY GUIDANCE SHOW ERIKA EVENTUALLY BECOMING A
HURRICANE...DESPITE THE SHEAR.

THE INITIAL MOTION ESTIMATE IS 300/8...THOUGH THE CENTER APPEARS TO
HAVE DONE SOME REFORMATION SINCE YESTERDAY. MID-LEVEL RIDGING
OVER THE WEST-CENTRAL ATLANTIC SHOULD CAUSE ERIKA TO MOVE ALONG
THAT GENERAL COURSE FOR THE NEXT COUPLE OF DAYS. THEREAFTER...
THE STORM COULD TURN MORE TO THE NORTHWEST AS IT NEARS THE
SOUTHWESTERN PERIPHERY OF THE RIDGE. THIS FORECAST IS RATHER
UNCERTAIN AS THE TRACK PROBABLY HAS A STRONG DEPENDENCE ON THE
FUTURE INTENSITY OF ERIKA. A WEAKER SYSTEM WOULD LIKELY MOVE MORE
TO THE WEST...SIMILAR TO THE UKMET OR GFS MODELS. HOWEVER...A
STRONGER SYSTEM WOULD LIKELY FEEL THE STRONG UPPER-LEVEL WINDS AND
MOVE MORE TO THE RIGHT...LIKE THE HWRF/GFDL. THE OFFICIAL FORECAST
IS LEFT OF THE DYNAMICAL CONSENSUS DUE TO THE STRONG SHEAR FORECAST
IN THE LONGER-TERM.

BECAUSE OF THE PROXIMITY TO THE NORTHERN LEEWARD ISLANDS...TROPICAL
STORM WATCHES HAVE BEEN ISSUED IN THAT AREA.


FORECAST POSITIONS AND MAX WINDS

INITIAL 01/2100Z 17.2N 57.3W 45 KT
12HR VT 02/0600Z 17.7N 58.2W 45 KT
24HR VT 02/1800Z 18.4N 60.3W 50 KT
36HR VT 03/0600Z 19.1N 62.0W 55 KT
48HR VT 03/1800Z 19.8N 63.8W 60 KT
72HR VT 04/1800Z 21.0N 66.5W 55 KT
96HR VT 05/1800Z 23.0N 69.5W 50 KT
120HR VT 06/1800Z 25.0N 72.0W 45 KT

$$
FORECASTER BLAKE/FRANKLIN