[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 290006
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST THU DEC 27 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC

...THE ITCZ...

THE ITCZ RUNS ALONG 6N10W AT LIBERIA TO 6N25W 3N37W 1S48W
INTO NE BRAZIL.  SCATTERED MODERATE CONVECTION IS WITHIN 120 NM
EITHER SIDE OF AXIS 29W-35W. CLUSTERS OF SHOWERS ARE WITHIN 120
NM OF EITHER SIDE OF AXIS 10W-29W AND 45-48W.

...DISCUSSION...

THE GULF OF MEXICO...
A MODEST COLD FRONT HAS BEEN PUSHING EASTWARD ACROSS THE GULF
DURING THE DAY.  LIGHTNING...COASTAL RADAR...AND IR IMAGERY
INDICATE THAT MODERATE CONVECTION EXTENDS ALONG A PRE-FRONTAL
SQUALL LINE...BUT THIS ONLY IS PRESENT OUT TO ABOUT 120 NM FROM
THE US GULF COAST.  NORTHERLY WINDS BEHIND THE FRONT ARE
GENERALLY ABOUT 10 KT...THOUGH SOME FUNNELING ALONG THE MEXICAN
COAST IS PRODUCING UP TO 20 KT OF WIND.  AHEAD OF THE
FRONT...WINDS ARE GENERALLY OUT OF THE SOUTH AT 10-15 KT.  IN
THE UPPER LEVELS...SOUTHWESTERLY FLOW DOMINATES REACHING 100 KT
ALONG THE NORTH GULF COAST ON THE SOUTH SIDE OF THE JET.  THE
CURRENT COOL AIR PUSH SHOULD BE SHORT-LIVED AND NOT EXTEND TO
THE EASTERN TWO-THIRDS OF THE GULF.  CYCLOGENESIS ALONG THE
NORTHERN GULF COAST SUNDAY MORNING SHOULD USHER IN ANOTHER BRIEF
PERIOD OF NORTHERLY WINDS AND COOLER TEMPS...THOUGH THIS APPEARS
TO BE SOMEWHAT STRONGER THAN THAT CURRENTLY IMPACTING THE GULF.
THE BIG EVENT LOOKS TO BE SET FOR TUESDAY AND WEDNESDAY WITH A
STRONG FRONT RACING ACROSS THE GULF WITH SOME GALE FORCE WINDS
PRESENT LIKELY IN THE WESTERN PART OF THE GULF.

THE CARIBBEAN SEA...
MOST OF THE CARIBBEAN IS CONVECTION FREE UNDER THE SUBSIDENT
ENVIRONMENT OF A UPPER-RIDGE CENTERED OVER JAMAICA.  THE
EXCEPTION IS AN AREA OF SCATTERED SHOWERS AND THUNDERSTORMS
ALONG AND JUST EAST OF CENTRAL AMERICA.  THIS MAY BE DUE TO THE
COMBINATION OF A WEAK SURFACE TROUGH AND UPPER-LEVEL
DIFFLUENCE.  SURFACE WINDS REMAIN EASTERLY AT 15-20 KT
THROUGHOUT MOST OF THE CARIBBEAN.  THE WINDS MAY BE ENHANCED
SOMEWHAT DURING THE NEXT DAY OR TWO AS THE PRESSURE GRADIENT
TIGHTENS OVER THE REGION AS THE HIGH OVER THE NORTH ATLANTIC
MOVES NORTH OF THE CARIBBEAN.  THE AFOREMENTIONED COLD FRONT
SHOULD LIKELY REACH THE NORTHWESTERN CARIBBEAN ON
WEDNESDAY...BRINGING MODERATE NORTHEASTERLY WINDS.

THE ATLANTIC OCEAN...
OF INTEREST IS THE DEEP CYCLONE CENTERED NEAR 26N38W.  THIS
SYSTEM HAS REMAINED STATIONARY FOR A COUPLE OF DAYS AND
ORGANIZED CONVECTION IS STARTING TO DEVELOP.  QUIKSCAT WINDS
SUGGEST THAT THERE ARE SOME GALE FORCE WINDS ALONG THE NORTHERN
SEMI-CIRCLE OF THE SYSTEM...BUT THERE MAY BE SOME RAIN
CONTAMINATION IN THE OBSERVED WINDS.  THE MAIN BAROCLINIC ZONE
REMAINS WELL TO THE NORTH OF THE SYSTEM AND ITS FRONTAL
STRUCTURE HAS TRANSITIONED TO A WEAK TRAILING TROUGH.  THE FSU
CYCLONE PHASE SPACE ANALYSES INDICATED THAT THE CYCLONE MAY BE
BECOMING A HYBRID SYSTEM...BUT UNTIL MORE SYMMETRIC DEEP
CONVECTION DEVELOPS IT WILL CONTINUE TO BE CONSIDERED AN
OCCLUDED LOW.  VERTICAL SHEAR ON THE SYSTEM IS RELATIVELY WEAK
AS THE UPPER PORTION OF THE CYCLONE IS DISPLACED SOMEWHAT
NORTHWEST OF THE SURFACE CIRCULATION.  THIS LOW-MODERATE SHEAR
ENVIRONMENT MAY ONLY LAST FOR ANOTHER DAY OR SO BEFORE STRONG
UPPER WESTERLIES IMPACT THE SYSTEM WITH THE APPROACH OF A
VIGOROUS SHORT-WAVE TROUGH.  THE CYCLONE SHOULD MEANDER IN PLACE
FOR THE NEXT TWO DAYS BEFORE MOVING OFF SLOWLY TO THE WEST OR
SOUTHWEST.  ELSEWHERE A WEAK SURFACE TROUGH IS PRODUCING
MODERATE SCATTERED WIDESPREAD CONVECTION BETWEEN 3-10N AND
42-50W.  AS WAS MENTIONED FOR THE GULF AND CARIBBEAN...A
VIGOROUS COLD FRONT WILL REACH THE WESTERN ATLANTIC SOUTH OF 31N
BY TUESDAY NIGHT-WEDNESDAY MORNING.

$$
CWL


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