[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 211758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 21 2008

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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...
TROPICAL WAVE IS TILTED ACROSS PUERTO RICO NEAR 19N66W THROUGH A
WEAK 1008 MB LOW NEAR 17N67W TO CURACAO. THIS SYSTEM IS SHOWING
SIGNS OF INCREASED ORGANIZATION...AND UPPER-LEVEL WINDS ARE
EXPECTED TO GRADUALLY BECOME MORE FAVORABLE FOR DEVELOPMENT TO
OCCUR OVER THE NEXT COUPLE OF DAYS. THIS SYSTEM COULD BECOME A
TROPICAL DEPRESSION AT ANY TIME AS IT MOVES SLOWLY N-NW OR
NORTHWARD AT ABOUT 4 KT. A BAND OF MODERATE TO STRONG CONVECTION
IS WITHIN 200 NM SE SEMICIRCLE OF LOW CENTER. LOCALLY HEAVY
RAINFALL AND STRONG GUSTY WINDS WILL AFFECT PUERTO RICO...THE
VIRGIN ISLANDS...AND THE NORTHERN LEEWARD ISLAND THROUGH MONDAY.
INTERESTS IN THESE AREAS SHOULD CLOSELY MONITOR PRODUCTS FROM
THEIR LOCAL WEATHER FORECAST OFFICE FOR ADDITIONAL INFORMATION
ON THIS SYSTEM.  A WIND GUST IN EXCESS OF 40 MPH WAS REPORTED AT
ST. THOMAS IN THE U.S. VIRGIN ISLANDS EARLIER TODAY...WITH A
RAINFALL AMOUNT OF 1.18 INCHES FOR THE PAST 24 HOURS.

...TROPICAL WAVES...
TROPICAL WAVE IS TILTED FROM 17N23W TO 6N26W S OF 17N MOVING W
10-15 KT. A BROAD CYCLONIC TURNING IS EVIDENT ON SATELLITE
IMAGERY. AN ASCAT PASS FROM AROUND 1100Z SHOWED NE WINDS OF 15
KT AHEAD OF THE WAVE AXIS...AND SE WINDS NEAR 10 KT BEHIND THE
WAVE LINE. SCATTERED MODERATE CONVECTION IS WITHIN 100 NM EITHER
SIDE OF THE WAVE AXIS.

TROPICAL WAVE IS ALONG 40W FROM 11N-19N MOVING W 10-15 KT. LOW
LEVEL CLOUDS INDICATE SOME INVERTED-V CURVATURE BETWEEN 12N-16N.
WAVE REMAINS EMBEDDED UNDER STRONG SUBSIDENCE AND A DRY...STABLE
AIR MASS ALOFT...THUS NO ASSOCIATED CONVECTIVE ACTIVITY.

TROPICAL WAVE IS ALONG 59W S OF 20N MOVING W 10-15 KT. VIS
SATELLITE IMAGERY SHOWS SOME INVERTED-V SIGNATURE JUST E OF THE
WINDWARD ISLANDS WITH MIDDLE TO HIGH LEVEL CLOUDINESS OBSERVED
NEAR THE NORTHERN END OF THE WAVE. THIS HIGH CLOUDS APPEARS TO
BE ASSOCIATED WITH THE ACTIVE TROPICAL WAVE/LOW LOCATED OVER THE
EASTERN CARIBBEAN. SEE SPECIAL FEATURE. ISOLATED SHOWERS ARE
SOUTH OF BARBADOS.

TROPICAL WAVE IS ALONG 85/86W S OF 21N MOVING W 10-15 KT. VIS
SATELLITE IMAGERY INDICATES A CLASSIC INVERTED-V PATTERN OVER
THE NW CARIBBEAN WITH SOME CYCLONIC TURNING OVER THE GULF OF
HONDURAS WHERE SCATTERED SHOWERS ARE NOTED.

...THE ITCZ...
ITCZ AXIS IS ANALYZED ALONG 11N15W 11N24W 8N35W 7N45W 8N58W.
ASIDE FROM CONVECTION ASSOCIATED WITH THE TROPICAL WAVE ALONG
26W...SCATTERED MODERATE CONVECTION IS FROM 8N-12N BETWEEN
28W-35W.

...DISCUSSION...

GULF OF MEXICO...
A SURFACE TROUGH REMAINS ACROSS THE WRN GULF OF MEXICO FROM
28N93W TO BAY OF CAMPECHE NEAR 19N94W. CONVECTION ASSOCIATED
WITH THIS TROUGH OVER THE BAY OF CAMPECHE IS CURRENTLY DYING
DOWN. THIS TROUGH IS FORECAST TO WEAKEN AND DRIFT WWD THROUGH
TUE. AN AREA OF SHOWERS WITH EMBEDDED TSTMS IS OVER THE EAST-
CENTRAL GULF FROM 24N-27N BETWEEN 86W-91W. UPPER DIFFLUENCE
BETWEEN AN UPPER-LEVEL TROUGH OVER TEXAS AND A BROAD UPPER LEVEL
RIDGE WHICH COVERS MOST OF THE GULF REGION IS ENHANCING ALL THIS
CONVECTIVE ACTIVITY. A SURFACE RIDGE DOMINATES THE SE CONUS AND
EXTENDS INTO THE FAR NRN GULF N OF 28N AND IS EXPECTED TO
CONTINUE BUILDING IN SLOWLY ACROSS THE NRN GULF WATERS THROUGH
MIDWEEK. A FRONTAL TROUGH FROM THE W ATLC CROSSES N FLORIDA AND
ENTERS THE GULF OF MEXICO JUST N OF TAMPA BAY. MODERATE NELY
WINDS ARE BLOWING ACROSS THE NORTHERN GULF WATERS.

CARIBBEAN SEA...
ALL THE ATTENTION REMAINS FOCUSED ON THE ERN CARIBBEAN TROPICAL
WAVE THAT CONTINUES TO BECOME BETTER ORGANIZED THIS MORNING. AN
AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT IS CURRENTLY ENROUTE
TO INVESTIGATE THE SYSTEM. INTERESTS IN PUERTO RICO...THE U.S.
AND BRITISH VIRGIN ISLANDS...AND EASTERN HISPANIOLA SHOULD
MONITOR THE PROGRESS OF THIS SYSTEM TO PROVIDE MORE INFORMATION
ON BOTH ITS STRUCTURE AND STRENGTH. SEE SPECIAL FEATURE FOR
MORE DETAILS. ANOTHER TROPICAL WAVE IS APPROACHING THE YUCATAN
PENINSULA AND BELIZE. THIS WAVE IS MOVING UNDER AN UPPER-LEVEL
RIDGE ANCHORED OVER SRN MEXICO EXTENDING ACROSS WESTERN CUBA AND
THE NW CARIBBEAN. UPPER DIFFLUENCE ASSOCIATED WITH THIS FEATURE
IS HELPING TO INDUCE SOME SHOWER ACTIVITY ALONG THE WAVE AXIS
OVER THE GULF OF HONDURAS. A SECOND UPPER-LEVEL RIDGE IS
ANCHORED JUST SOUTH OF HAITI EXTENDING E ACROSS THE LESSER
ANTILLES INTO THE W TROPICAL ATLC. IN THE MIDDLE...THERE IS AN
INVERTED TROUGH THAT RUNS FROM CENTRAL CUBA TO THE
NICARAGUA/HONDURAS BORDER.  THESE UPPER LEVEL FEATURES ARE
ENHANCING SCATTERED SHOWER ACTIVITY ACROSS MUCH OF THE BASIN.

ATLANTIC OCEAN...
A NARROW UPPER-LEVEL TROUGH IS OVER THE FAR W ATLC EXTENDING
THROUGH 31N75W TO OVER THE CENTRAL BAHAMAS AND CUBA INTO THE
CARIBBEAN SEA. THIS FEATURE ALOFT SUPPORTS A FRONTAL TROUGH THAT
ENTERS THE AREA NEAR 31N75W THEN CONTINUES SW ACROSS N FLORIDA.
SCATTERED SHOWERS/ISOLATED TSTMS ARE WITHIN 80-100 NM EITHER
SIDE OF THE TROUGH. A PAIR OF UPPER LOWS ARE TO THE EAST ACROSS
THE W-CENTRAL ATLC CENTERED NEAR 26N63W AND 25N48W. STRONG SWLY
FLOW AHEAD OF THIS SECOND UPPER LEVEL LOW IS PRODUCING SOME HIGH
CLOUDINESS ACROSS THE CENTRAL ATLC N OF 20N. THE UPPER RIDGE
OVER THE ERN CARIBBEAN EXTENDS ACROSS THE LEEWARD ISLANDS TO
OVER THE W TROPICAL ATLC NEAR 17N56W. WEAK UPPER TROUGHING IS
OVER THE NE ATLC EXTENDING FROM A DEEP LAYERED LOW N OF THE
REGION TO 25N E OF 25W TO OVER THE CANARY ISLANDS. AN E/W UPPER
RIDGE CENTERED OVER THE CAPE VERDE ISLANDS CONTROLS THE
REMAINDER OF THE TROPICAL ATLC TO 35W S OF THE UPPER TROUGHING
ACROSS THE NE ATLC. AT THE SURFACE...MOST OF THE DISCUSSION
AREA...MAINLY N OF 20N AND W OF 70W IS DOMINATED BY A STATIONARY
1025 MB SURFACE HIGH SITUATED NEAR 35N51W.

$$
GR





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