[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 161734
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST TUE DEC 16 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
1645 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 6N8W 3N22W 3N43W 2N51W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 90 NM S OF THE
ITCZ FROM 26W-29W. LARGE CLUSTERS OF SIMILAR CONVECTION ARE
WITHIN 75 NM OF LINE FROM 6N18W 5N30W TO 9N43W.

...DISCUSSION...

GULF OF MEXICO...
MODERATE/STRONG WLY MID/UPPER FLOW COVERS THE GULF WITH STRONGER
WINDS OVER THE GULF COAST STATES FROM LOUISIANA TO GEORGIA ON
THE N PERIPHERY OF AN UPPER RIDGE EXTENDING FROM THE W
CARIBBEAN. THIS FLOW CONTINUES TO SPREAD PACIFIC HIGH LEVEL
MOISTURE ACROSS THE N GULF WITH DRIER AIR PRESENT IN LIGHTER
FLOW OVER THE S HALF. IN THE LOWER LEVELS...A SURFACE RIDGE OVER
THE NW ATLC CONTINUES PRODUCING SELY FLOW OVER THE FAR E GULF
AND LOW LEVEL ISOLATED SHOWERS IN THE FLORIDA STRAITS S OF THE
FLORIDA KEYS AND ALONG THE E COAST OF FLORIDA. A COLD FRONT
ENTERS THE GULF THROUGH A 1023 MB LOW OVER S MISSISSIPPI ACROSS
THE MISSISSIPPI DELTA OF LOUISIANA SW TO 27N95W THEN S TO INLAND
OVER MEXICO NEAR TAMPICO THEN N ALONG THE E SLOPES OF THE SIERRA
MADRE MOUNTAINS. THIS FRONT IS BEGINNING TO LOSE ITS UPPER
SUPPORT CAUSING THE FRONT TO STALL THEN PUSH NW AS THE SURFACE
RIDGE OVER THE ATLC AGAIN GAINS CONTROL OF THE GULF. SCATTERED
SHOWERS ARE N OF 27N FROM PANAMA CITY FLORIDA TO THE MISSISSIPPI
DELTA WITH DENSE LOW LEVEL CLOUD COVER AND POSSIBLE ISOLATED
SHOWERS W OF THE FRONTAL BOUNDARY.

CARIBBEAN SEA...
ABUNDANT STABLE AIR ALOFT DOMINATES MUCH OF THE CARIBBEAN WITH
SOME POCKETS OF UPPER LEVEL MOISTURE OVER THE SW CARIBBEAN AND
CENTRAL AMERICA. THE W CARIBBEAN IS DOMINATED BY AN UPPER RIDGE
EXTENDS FROM PANAMA OVER CENTRAL AMERICA AND INTO THE GULF OF
MEXICO. THE UPPER TROUGH OVER THE CENTRAL ATLC REMAINS OVER THE
E CARIBBEAN ACROSS THE LESSER ANTILLES INTO THE W TROPICAL ATLC.
THE PRESSURE GRADIENT BETWEEN STRONG SURFACE RIDGE OVER THE W
ATLC AND RELATIVE LOWER PRESSURE OVER THE CARIBBEAN CONTINUES TO
MAINTAIN MODERATE/STRONG ELY TRADE WINDS ACROSS THE AREA THAT
ARE EXPECTED TO GRADUALLY DIMINISH STARTING TONIGHT INTO WED.
TYPICAL PATCHES OF LOW LEVEL CLOUDS AND EMBEDDED QUICK MOVING
ISOLATED SHOWERS ARE BEING DRIVEN BY THE TRADE WINDS...BUT THE
LARGE SCALE SUBSIDENT ENVIRONMENT IS KEEPING THE MOISTURE
SHALLOW.

ATLANTIC OCEAN...
THE UPPER RIDGE THAT COVERS THE W CARIBBEAN AND THE GULF OF
MEXICO EXTENDS OVER THE W ATLC W OF 70W. THE SURFACE RIDGE OVER
THE NW ATLC CONTINUES TO PRODUCE LOW LEVEL ISOLATED SHOWERS
ACROSS THE W ATLC TO ALONG THE E COAST OF FLORIDA. A COMPLEX
UPPER TROUGH REMAINS OVER THE CENTRAL ATLC WITH AN EMBEDDED
UPPER LOW NEAR 23N59W AND CONTINUES TO PROVIDE LIMITED SUPPORT
FOR A WEAKENING STATIONARY FRONT EXTENDING THROUGH 32N53W TO
23N59W. A WEAKENING 1012 MB LOW IS JUST TO THE S OF THE FRONT
NEAR 29N56W WITH A SURFACE TROUGH EXTENDING THROUGH A DEVELOPING
1010 MB LOW NEAR 26N53W THEN INTO THE TROPICS ALONG 21N55W TO
16N56W. THE TIGHT PRESSURE GRADIENT BETWEEN THIS COMPLEX SURFACE
SYSTEM AND THE SURFACE RIDGES OVER THE W AND E ATLC ARE
PRODUCING NLY GALE FORCE WINDS N OF 27N W OF FRONT TO 60W AND
20-25 KT ELSEWHERE W OF THE FRONT. SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS WITHIN 90/120 NM OF SURFACE TROUGH N OF
23N AND WITHIN 75 NM OF THE FRONTAL BOUNDARY. SIMILAR ACTIVITY
IS WITHIN 200 NM OF LINE FROM 23N45W TO BEYOND 32N51W IN AN
UPPER DIFFLUENT ZONE. THE FRONT IS EXPECTED TO GRADUALLY WEAKEN
AS THE 1010 MB SURFACE LOW AND SHOULD TRACK W THEN SW OVER THE
NEXT FEW DAYS OPENING UP INTO A TROUGH LATE THU NEAR THEN SE
GREATER ANTILLES.

$$
WALLACE



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