[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 012357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE SEP 01 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2330 UTC.

...SPECIAL FEATURES...

A TROPICAL SYSTEM E OF THE LESSER ANTILLES HAS BEEN UPGRADED TO
TROPICAL STORM ERIKA AS OF 01/2100 UTC. AS OF 02/0000 UTC
TROPICAL STORM ERIKA HAS BARELY MOVED FROM ITS PREVIOUS POSITION
AND IS CENTERED NEAR 17.2N 57.3W...OR ABOUT 390 MILES E OF THE
NRN LEEWARD ISLANDS. ERIKA HAS BEEN MEANDERING FROM THE PAST 3
HOURS BUT IS EXPECTED TO BEGIN MOVING WNW NEAR 8 KT. ESTIMATED
CENTRAL PRESSURE IS 1004 MB REPORTED BY AN AIR FORCE RESERVE
RECONNAISSANCE AIRCRAFT. MAXIMUM SUSTAINED WINDS ARE 45 KT WITH
GUSTS TO 55 KT. PLEASE SEE THE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21. TROPICAL STORM FORCE
WINDS EXTEND OUTWARD UP TO 105 MILES. NUMEROUS STRONG CONVECTION
IS FROM 15N-19N BETWEEN 53W-58W. INTERESTS IN THE NRN LEEWARD
ISLANDS...U.S. AND BRITISH VIRGIN ISLANDS...AND PUERTO RICO
SHOULD MONITOR THE PROGRESS OF ERIKA.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 20W/21W S OF 20N MOVING W 15-20 KT.
UPPER AIR TIME-SECTION ANALYSIS FROM DAKAR SENEGAL INDICATED
THAT THIS WAVE PASSED DAKAR AROUND 01/0000 UTC. SATELLITE
IMAGERY INDICATES LOW-LEVEL CYCLONIC FLOW IN THE VICINITY OF THE
WAVE AXIS. THE WAVE ALSO COINCIDES WITH A DEEP LAYER MOISTURE
MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS W OF THE WAVE AXIS FROM
12N-18N BETWEEN 22W-25W. THIS SYSTEM HAS A LOW CHANCE...LESS
THAN 30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT
48 HRS.

A TROPICAL WAVE EXTENDS FROM 16N39W TO 8N35W MOVING W NEAR 20
KT. THE WAVE IS ALONG THE LEADING EDGE OF A MAXIMUM IN DEEP
LAYER MOISTURE OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY.
LOW-LEVEL CYCLONIC FLOW IS IN THE VICINITY OF THE WAVE AXIS AS
NOTED IN SATELLITE IMAGERY AND SATELLITE DERIVED WINDS.
HOWEVER...THE WAVE IS EMBEDDED WITHIN A DRY SAHARAN AIR LAYER
WHICH IS CURRENTLY INHIBITING ANY DEEP CONVECTION NEAR THE WAVE
AXIS.

A TROPICAL WAVE IS ALONG 86W S OF 14N MOVING W NEAR 20 KT. THIS
WAVE CONTINUES TO BE LOCATED BASED ON CONTINUITY AS THERE IS NO
CLEAR SIGNATURE IN SURFACE OBSERVATIONS OR SATELLITE IMAGERY.
HOWEVER...SCATTERED MODERATE/ISOLATED STRONG CONVECTION HAS
RECENTLY POPPED UP NEAR THE WAVE AXIS FROM 10N-16N BETWEEN
84W-86W. THIS ACTIVITY IS PROBABLY ASSOCIATED MORE WITH UPPER
LEVEL DIFFLUENCE THAN SURFACE CONVERGENCE NEAR THE WAVE.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 14N16W 11N28W 12N35W 9N44W
11N51W. ISOLATED MODERATE CONVECTION IS WITHIN 200NM S OF THE
AXIS BETWEEN 37W-48W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A STATIONARY FRONT LINES THE NRN GULF FROM
THE FLORIDA PANHANDLE TO SRN TEXAS EXTENDING ALONG 31N82W 30N86W
28N90W 28N97W. ISOLATED SHOWERS ARE WITHIN 200NM AHEAD OF THE
FRONT. A SURFACE TROUGH IS ACROSS S FLORIDA FROM A 1014 MB LOW
NEAR 26N81W EXTENDING INTO THE SE GULF ALONG 24N83W 23N88W.
SURFACE CONVERGENCE NEAR THIS TROUGH IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS THE FLORIDA PENINSULA E OF 83W.
BASED ON RECENT LIGHTNING DATA THE MOST ACTIVITY IS LOCATED OVER
SRN FLORIDA NEAR THE SURFACE LOW. ANOTHER SURFACE TROUGH IS
ACROSS THE YUCATAN PENINSULA AND THE BAY OF CAMPECHE EXTENDING
FROM 22N93W TO 17N89W. SURFACE CONVERGENCE NEAR THE TROUGH IS
SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN
PENINSULA...AND ISOLATED SHOWERS ACROSS THE BAY OF CAMPECHE AND
W GULF W OF 93W S OF 25N. IN THE UPPER LEVELS...AN UPPER LEVEL
TROUGH IS OVER THE NRN GULF N OF 27N SUPPORTING THE STATIONARY
FRONT. AN UPPER LEVEL RIDGE COVERS THE REMAINDER OF THE GULF
CENTERED OVER MEXICO NEAR 22N102W. THE WIDTH OF THE RIDGE
NARROWS ACROSS THE SE GULF AND EXTENDS ACROSS S FLORIDA AND INTO
THE ATLC. UPPER LEVEL DIVERGENCE BETWEEN THE UPPER RIDGE AND
UPPER TROUGH IS ENHANCING THE AFOREMENTIONED AREAS OF
SHOWERS/THUNDERSTORMS.

CARIBBEAN SEA...
AN UPPER LEVEL RIDGE COVERS THE WRN CARIBBEAN CENTERED NEAR
17N83W. UPPER LEVEL DIFFLUENCE BETWEEN THIS RIDGE AND AN UPPER
LEVEL TROUGH S OF CENTRAL AMERICA IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS ERN HONDURAS AND NRN NICARAGUA.
ISOLATED SHOWERS ARE ALSO ACROSS THE FAR NW CARIBBEAN. UPPER
LEVEL DIFFLUENCE BETWEEN THE UPPER RIDGE AND A SHORTWAVE UPPER
TROUGH EXTENDING LATERALLY ACROSS CUBA FROM A LARGER UPPER LEVEL
TROUGH OVER THE ATLC ACROSS HISPANIOLA AND INTO THE CENTRAL
CARIBBEAN IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS
CUBA AND THE ADJACENT COASTAL WATERS. A SURFACE TROUGH ACROSS
THE CENTRAL BAHAMAS EXTENDS TO NRN CUBA NEAR 21N76W. SURFACE
CONVERGENCE NEAR THE TROUGH IS ALSO ENHANCING THE SHOWER
ACTIVITY ACROSS CUBA. ELSEWHERE ACROSS THE CARIBBEAN...DRY AIR
AND SUBSIDENCE ALOFT IS SUPPORTING GENERALLY FAIR WEATHER
BESIDES A FEW ISOLATED SHOWERS E OF 66W DUE TO MOIST SLY FLOW
ALOFT AROUND AN UPPER LEVEL RIDGE E OF THE LESSER ANTILLES.
MODERATE TO FRESH TRADE WINDS ARE ACROSS MUCH OF THE BASIN WITH
STRONGER WINDS NEAR THE COAST OF COLUMBIA. INTERESTS IN THE NRN
LEEWARD ISLANDS...U.S. AND BRITISH VIRGIN ISLANDS...AND PUERTO
RICO SHOULD MONITOR THE PROGRESS OF TROPICAL STORM ERIKA...SEE
SPECIAL FEATURES ABOVE.

ATLANTIC OCEAN...
THE MAIN FOCUS FOR THE ATLC BASIN TONIGHT IS TROPICAL STORM
ERIKA. SEE SPECIAL FEATURES ABOVE. IN THE W ATLC...AS OF 2100
UTC...A STATIONARY FRONT EXTENDS ACROSS THE NRN GULF TO NRN
FLORIDA NEAR 31N81W EXTENDING OUT OF THE DISCUSSION AREA NEAR
32N77W. A SURFACE TROUGH IS OUT AHEAD OF THE FRONT FROM A 1014
MB LOW OVER S FLORIDA NEAR 26N81W EXTENDING TO 31N78W. SURFACE
CONVERGENCE NEAR THE FRONT AND SURFACE TROUGH IS SUPPORTING
SCATTERED SHOWERS/THUNDERSTORMS NW OF A LINE FROM 24N81W TO
31N71W. RECENT LIGHTNING ACTIVITY INDICATES THAT THE MOST ACTIVE
THUNDERSTORMS ARE LOCATED OVER S FLORIDA AND THE ADJACENT
WATERS. A SURFACE TROUGH EXTENDS FROM NRN CUBA NEAR 21N76W TO
28N74W. SURFACE CONVERGENCE NEAR THIS TROUGH IS SUPPORTING
SCATTERED SHOWERS/THUNDERSTORMS ACROSS CUBA...AND ISOLATED
SHOWERS ACROSS THE BAHAMAS AND HISPANIOLA FROM 19N-27N W OF 68W.
ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE DOMINATES
ANCHORED BY A 1031 MB HIGH NEAR 36N39W. IN THE UPPER LEVELS...AN
UPPER LEVEL TROUGH IS OVER THE ERN CONUS WHILE A SHORTWAVE UPPER
RIDGE EXTENDS ACROSS S FLORIDA CONTINUING ALONG 27N80W TO
38N62W. UPPER LEVEL DIFFLUENCE BETWEEN THESE FEATURES IS
SUPPORTING THE SHOWER ACTIVITY IN THE WRN ATLC. E OF THE UPPER
RIDGE AN UPPER LEVEL TROUGH EXTENDS ALONG 35N57W TO HISPANIOLA
CONTINUING INTO THE CENTRAL CARIBBEAN. AN UPPER LEVEL RIDGE IS E
OF THE LESSER ANTILLES CENTERED NEAR 18N51W SUPPORTING TROPICAL
STORM ERIKA. A LATERALLY ORIENTED UPPER LEVEL TROUGH DOMINATES
THE E ATLC WITH AXIS ALONG 25N. ACROSS THE TROPICAL ATLC...AN
UPPER LEVEL RIDGE IS S OF 20N E OF 32W.


ENTERS THE DISCUSSION AREA NEAR 31N81
AND EXTENDS TO NEAR SAINT AUGUSTINE FLORIDA. A PRE-FRONTAL
TROUGH IS ALSO ANALYZED S OF THE FRONTAL BOUNDARY FROM 32N77W TO
WEST PALM BEACH FLORIDA. SCATTERED SHOWERS AND TSTMS ARE
OCCURRING WITHIN 150 NM E OF THE SURFACE TROUGH N OF 27N.
FARTHER TO THE E...AN UPPER LEVEL LOW IS CENTERED N OF THE AREA
NEAR 33N61W AND EXTENDS TROUGHING SW TO OVER HISPANIOLA AND INTO
THE CENTRAL CARIBBEAN. A SURFACE TROUGH IS ANALYZED FROM 27N76W
TO THE WINDWARD PASSAGE. SCATTERED SHOWERS AND ISOLATED TSTMS
ARE OCCURRING E OF THE SURFACE TROUGH FROM 20N-26N BETWEEN
67W-73W. ELSEWHERE ACROSS THE REMAINDER OF THE CENTRAL AND ERN
ATLC...THE BASIN REMAINS FAIRLY BENIGN AS A SURFACE RIDGE
CONTROLS N OF 20N E OF 65W AND IS ANCHORED BY A 1031 MB SURFACE
HIGH CENTERED N OF THE REGION WSW OF THE AZORES NEAR 37N36W.

$$
HUFFMAN




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