[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 210543
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST FRI DEC 21 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 5N9W 3N20W 4N30W 3N40W AND INTO
SOUTH AMERICA NEAR THE EQUATOR AND 50W. CLUSTERS OF MODERATE TO
STRONG CONVECTION ARE WITHIN 120 NM N OF THE AXIS BETWEEN
22W-30W. SCATTERED MODERATE CONVECTION IS BETWEEN 1N-8N AND
33W-39W. UPPER DIFFLUENCE IS ENHANCING CONVECTION ALONG THE ITCZ.

DISCUSSION...
GULF OF MEXICO...
THE GULF IS QUITE ACTIVE THIS MORNING WITH A COLD FRONT ENTERING
THE REGION NEAR 30N92W AND EXTENDING SSW TO 26N95W THEN WSW INTO
MEXICO NEAR 25N98W. A LARGE BAND OF SHOWERS AND THUNDERSTORMS
EXTENDS AHEAD OF THE FRONT AFFECTING THE NORTH CENTRAL AND EAST
GULF N OF 25N E OF 90W. AS OF 03Z A 1008 MB LOW WAS ANALYZED IN
THE CONVECTIVE AREA NEAR 30N85W WITH A SFC TROUGH EXTENDING FROM
THE LOW CENTER THROUGH THE CONVECTION ALONG 28N85W 27N86W AND
27N89W. MODERATE TO STRONG S TO SW WINDS ARE BLOWING AHEAD OF
THE FRONT AND SHIP OBS INDICATE 20-30 KT NEAR THE SFC TROUGH.
WINDS WILL SHIFT TO THE NW IN THE WAKE OF THE FRONT. A RIDGE OF
HIGH PRESSURE CONTINUES TO DOMINATE THE REMAINDER OF THE GULF.
ALOFT...A SHORT-WAVE TROUGH MOVING EWD ACROSS THE LOWER
MISSISSIPPI VALLEY SUPPORTS THE COLD FRONT. A SUBTROPICAL JET
WITH CORE WINDS OF NEAR 110 KT IS CENTERED OVER THE N GULF
WATERS/N FLORIDA DRAWING UPPER-LEVEL MOISTURE ACROSS THE GULF
FROM THE E PACIFIC. NEAR ZONAL FLOW SOUTH OF THE JET CONTINUES
TO MAINTAIN DRY AND STABLE CONDITIONS. A STRONGER COLD FRONT IS
EXPECTED TO MOVE INTO THE NW GULF SAT EVENING. MODERATE TO
STRONG NLY WINDS AND BUILDING SEAS CAN BE EXPECTED BEHIND FRONT.

CARIBBEAN SEA...
TRANQUIL WEATHER CONDITIONS PERSIST ACROSS THE CARIBBEAN THIS
EVENING UNDER THE INFLUENCE OF A MID/UPPER-LEVEL RIDGE WHICH IS
PRODUCING STRONG SUBSIDENCE AND A DRY/STABLE AIRMASS.  ONLY A
FEW PATCHES OF LOW LEVEL CLOUDS WITH ISOLATED SHOWERS REMAIN
OVER THE AREA. TYPICAL FRAGMENTS OF MOISTURE ARE BRINGING
ISOLATED PASSING SHOWERS TO THE NE CARIBBEAN...INCLUDING PUERTO
RICO AND THE SURROUNDING ISLANDS. ADDITIONAL POCKETS OF MOISTURE
ARE STREAMING ACROSS NICARAGUA AND COSTA RICA UNDER A NELY FLOW.
LIGHT TO MODERATE TRADES WILL PREVAIL OVER MUCH OF THE AREA
THROUGH MONDAY.

ATLANTIC OCEAN...
A WEAK PRESSURE GRADIENT IN THE W ATLC IS MAINTAINING LIGHT
WINDS ACROSS THE REGION. INCREASING WINDS AND SEAS ARE EXPECTED
AS THE GRADIENT TIGHTENS BETWEEN BUILDING HIGH PRESSURE TO THE
NORTH AND A LOW PRESSURE MOVING ACROSS FLORIDA. A WEAK COLD
FRONT CLIPS THE DISCUSSION AREA ALONG 31N BETWEEN 70W-78W. A
PRE-FRONTAL TROUGH IS ANALYZED FROM 32N63W TO 27N67W. PATCHES OF
LOW CLOUDS SURROUND THE TROUGH. FARTHER EAST...A WEAK SFC LOW IS
CENTERED NEAR 28N56W. A STATIONARY FRONT EXTENDS FROM THE LOW
ALONG 30N54W 31N45W AND 31N34W THEN CONTINUES NE AS A COLD FRONT
PASSING E OF THE AZORES. A SFC TROUGH EXTENDS FROM THE LOW
CENTER ALONG 24N58W 21N63W THEN CONTINUES WESTWARD TO THE
BAHAMAS NEAR 21N74W. SATELLITE IMAGERY DEPICTS A LARGE AREA OF
SHOWERS WITH ISOLATED TSTMS WITHIN 130 NM EITHER SIDE OF THE
FRONTAL BOUNDARY. A LARGE RIDGE OF HIGH PRESSURE IS OVER THE
CENTRAL AND E ATLC. FAIR WEATHER STRATOCUMULUS CLOUDS ARE BEING
TRANSPORTED AROUND THE RIDGE. A FRONTAL BOUNDARY ASSOCIATED WITH
A DEEP-LAYERED TROUGH OVER THE E ATLC HAS MOVED E OVER THE
AFRICAN COAST. IN THE TROPICAL ATLC...DIFFLUENCE ASSOCIATED WITH
AN UPPER-LEVEL HIGH LOCATED OVER NE BRAZIL IS SUPPORTING
CONVECTION ALONG THE ITCZ AND NEAR ZONAL FLOW CONTINUES TO
TRANSPORT UPPER-LEVEL MOISTURE EASTWARD ACROSS THE REGION S OF
14N. A SFC TROUGH IS JUST EAST OF THE WINDWARD ISLANDS ALONG 59W
FROM 8N-14N. SCATTERED MODERATE CONVECTION IN THIS AREA IS
ENHANCED BY UPPER DIFFLUENCE. THIS SHOWER ACTIVITY IS AFFECTING
THE WINDWARD ISLANDS AND NE VENEZUELA.

$$
GR/RJW







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