[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 171757
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST WED DEC 17 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 8N12W 4N22W 5N43W 3N51W. BROAD AREA OF
SCATTERED MODERATE WITH EMBEDDED CLUSTERS OF SCATTERED STRONG
CONVECTION ARE FROM 1N-7N BETWEEN 15W-35. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 4N-6N BETWEEN
37W-41W.

...DISCUSSION...

GULF OF MEXICO...
MODERATE WLY MID/UPPER FLOW COVERS THE GULF ON THE N PERIPHERY
OF AN UPPER RIDGE EXTENDING FROM CENTRAL AMERICA COVERING THE W
CARIBBEAN AS WELL AS MEXICO. IN THE LOWER LEVELS...A STATIONARY
FRONT ENTERS THE GULF ACROSS CENTRAL LOUISIANA SSW TO INLAND
OVER MEXICO N OF TAMPICO THEN N ALONG THE E SLOPES OF THE SIERRA
MADRE MOUNTAINS. THIS FRONT HAS LOST ITS UPPER SUPPORT. THE
SURFACE RIDGE IS ONCE AGAIN IN CONTROL OF THE REMAINDER OF THE
GULF. DENSE LOW LEVEL CLOUD COVER AND SCATTERED/ISOLATED SHOWERS
ARE W OF THE FRONTAL BOUNDARY WITH LOW LEVEL ISOLATED SHOWERS
MOVING ACROSS S FLORIDA AND THROUGH THE FLORIDA STRAITS ON THE
ELY SURFACE FLOW.

CARIBBEAN SEA...
ABUNDANT STABLE AIR ALOFT DOMINATES THE CARIBBEAN INCLUDING
CENTRAL AND PORTIONS OF SOUTH AMERICA. THE W CARIBBEAN IS
DOMINATED BY AN UPPER RIDGE THAT EXTENDS FROM THE E PACIFIC
REGION ACROSS CENTRAL AMERICA AND INTO THE GULF OF MEXICO. THE
UPPER TROUGH OVER THE W/CENTRAL ATLC REMAINS OVER THE REMAINDER
OF THE CARIBBEAN E OF 75W ACROSS THE LESSER ANTILLES INTO THE W
TROPICAL ATLC. THE PRESSURE GRADIENT BETWEEN SURFACE RIDGE OVER
THE W ATLC AND RELATIVE LOWER PRESSURE OVER THE W CARIBBEAN
CONTINUES TO MAINTAIN MODERATE/STRONG ELY TRADE WINDS ACROSS THE
AREA W OF 75W. TYPICAL PATCHES OF LOW LEVEL CLOUDS AND EMBEDDED
QUICK MOVING ISOLATED SHOWERS ARE BEING DRIVEN BY THESE 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 75W. THE SURFACE RIDGE OVER
THE NW ATLC CONTINUES TO PRODUCE MODERATE ELY WINDS ACROSS THE W
ATLC AND GENERATING LOW LEVEL ISOLATED SHOWERS TO ALONG THE E
COAST OF FLORIDA. AN UPPER TROUGH REMAINS OVER THE W/CENTRAL
ATLC WITH AN EMBEDDED UPPER LOW CO-LOCATED WITH A 1008 MB
SURFACE LOW NEAR 25N59W AND A SURFACE TROUGH EXTENDING FROM
31N56W THROUGH THE SURFACE LOW TO 20N61W. THE TIGHT PRESSURE
GRADIENT BETWEEN THIS SURFACE SYSTEM AND THE SURFACE RIDGES OVER
THE FAR W AND ALL OF THE E ATLC ARE KEEPING NLY GALE FORCE WINDS
N OF 25N BETWEEN 58W-67W BUT ARE EXPECTED TO BE BELOW GALE FORCE
IN THE NEXT FEW HOURS. PATCHES OF SCATTERED SHOWERS AND POSSIBLE
ISOLATED THUNDERSTORMS ARE N OF 24N BETWEEN 50W-65W. THE SURFACE
LOW SHOULD TRACK SW OPENING UP INTO A TROUGH THU JUST NE OF THE
LEEWARD ISLANDS.

$$
WALLACE



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