[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 300003
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST FRI DEC 29 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

...SPECIAL FEATURE...

THE WELL-DEFINED NON-BAROCLINIC CYCLONE CONTINUES IN THE
NORTHEAST ATLANTIC NEAR 28N38W.  THE SYSTEM HAS BEEN DRIFTING
NORTH-NORTHEASTWARD DURING THE DAY AND HAS DEVELOPED PRONOUNCED
ANTICYCLONIC OUTFLOW IN THE UPPER TROP.  DESPITE WATER
TEMPERATURES NEAR THE CYCLONE OF AROUND 22-23C...MODERATE
CONVECTION HAS BEEN PERSISTENT ON THE NORTHEAST SEMICIRCLE.
SATELLITE CLASSIFICATIONS SUGGEST THAT THE SYSTEM COULD BE A
MINIMAL SUBTROPICAL STORM.  QUIKSCAT WINDS...WHILE HAVING THE
USUAL AMBIGUITY ISSUES IN RAINY CONDITIONS...INDICATE THAT GALE
FORCE WINDS LIKELY ARE OCCURRING IN THE NORTHERN SEMICIRCLE.
TROPOSPHERIC VERTICAL SHEAR IS ABOUT 20 KT AS THE STRONGEST
UPPER TROP WESTERLIES ARE BYPASSING THE CYCLONE TO THE NORTH AND
THE SOUTH.  THE CYCLONE SHOULD MEANDER OVER THE NEXT 36 HOURS
BEFORE BEING PUSHED OFF TOWARD THE WEST OR SOUTHWEST BY A
DEVELOPING MID-OCEAN RIDGE ON MONDAY.  GIVEN THAT THE VERTICAL
SHEAR SHOULD INCREASE SUBSTANTIALLY TOMORROW...TONIGHT MAY BE
THE LAST OPPORTUNITY FOR THIS SYSTEM TO GAIN A BIT MORE
ORGANIZATION TO ITS CONVECTION AND MAKE THE TRANSITION TO A
NAMED SUBTROPICAL STORM.

...THE ITCZ...

ITCZ AXIS IS LOCATED ALONG 6N11W AT THE LIBERIA COAST 3N16W
3N30W INTO NE BRAZIL NEAR 2S45W. WIDELY SCATTERED MODERATE
CONVECTION IS WITHIN 60 NM OF THE ITCZ AXIS BETWEEN 30W-38W.
WIDELY SCATTERED SHOWERS ARE ALSO FOUND WITHIN 120 NMI OF THE
ITCZ AXIS ELSEWHERE.

...DISCUSSION...

THE GULF OF MEXICO...
AS OF 2100 UTC...A FRONTAL BOUNDARY EXTENDS ACROSS THE GULF OF
MEXICO FROM THE FLORIDA PANHANDLE TO THE BAY OF CAMPECHE.  SOUTH
OF 28N...THE FRONT HAS STALLED OUT AND IS WEAKENING.  IN THE
UPPER LEVELS...SOUTHWESTERLIES PREVAIL OVER THE GULF RANGING
FROM 40 KT IN THE SE TO 90 KT IN THE NW GULF.  NORTH OF 28N AND
INTO THE FLORIDA PANHANDLE...THE FRONT IS SLIGHTLY PROGRESSIVE
AND IS CONSIDERED A COLD FRONT.  LIGHTNING...IR SATELLITE...AND
RADAR IMAGERY SHOW THAT THE FRONT IS CONVECTIVE ACTIVE NORTH OF
26N.  WINDS BEHIND THE FRONT ARE NORTHEAST TO NORTH 15 KT OR
LESS.  WINDS AHEAD OF THE FRONT ARE SOUTHEAST TO SOUTH ABOUT 10
KT OR LESS.  THE CURRENT FRONTAL BOUNDARY SHOULD LIKELY
DISSIPATE TONIGHT OR EARLY TOMORROW TO BE REPLACED BY A NEWLY
EMERGING FRONT REACHING THE NORTHWEST GULF OF MEXICO TOMORROW.
THIS NEW COOL AIR MASS SHOULD BE SHORT-LIVED AND NOT LIKELY TO
PUSH ACROSS THE WHOLE GULF.  A MUCH MORE VIGOROUS COLD FRONT
WILL IMPACT THE GULF ON TUESDAY WITH THE ENTIRE REGION
EXPERIENCING STRONG NORTHERLY WINDS WITH SOME GALES EXPECTED IN
THE WESTERN GULF.

THE CARIBBEAN SEA...
THE CARIBBEAN IS EXPERIENCING NO LARGE-SCALE AREAS OF CONVECTION
CURRENTLY...AS THE REGION IS BEING DOMINATED BY SUBSIDENCE FROM
A UPPER LEVEL RIDGE CENTERED NEAR JAMAICA.  THE RIDGE IS
BECOMING MORE HIGH AMPLITUDE AS A STRONG SHORT-WAVE TROUGH IS
IMPINGING ON THE REGION WITH THE TROUGH AXIS A COUPLE HUNDRED NM
EAST OF THE LESSER ANTILLES.  SURFACE WINDS ARE 15 TO 25 KT
EASTERLY...WITH THE STRONGER WINDS IN THE CENTRAL CARIBBEAN
NORTH OF THE COLOMBIAN COAST.  SOME WEAKENING OF THE WINDS ARE
EXPECTED AS THE PRESSURE GRADIENT RELAXES.  THE AFOREMENTIONED
VIGOROUS COLD FRONT WILL REACH THE NORTHWESTERN CARIBBEAN ON
WEDNESDAY MORNING AND WILL CAUSE MODERATE NORTH TO NORTHEAST
WINDS ON WEDNESDAY AND THURSDAY.

THE ATLANTIC OCEAN...
A 1006 MB LOW IS NEAR 28N38W. SEE SPECIAL FEATURE ABOVE FOR
DETAILS.  ELSEWHERE...SURFACE RIDGING IS IN PLACE THROUGHOUT THE
REST OF THE REGION WITH EAST TO NORTHEAST WINDS 15 TO 20 KT
GENERALLY.  WIDELY SCATTERED MODERATE CONVECTION CONTINUES IN
ASSOCIATION WITH A WEAK SURFACE TROUGH ALONG 40W BETWEEN
4N-11N.  THE STRONG UPPER LEVEL TROUGH MENTIONED IN THE PREVIOUS
SECTION IS HELPING TO PRODUCE WIDESPREAD BUT ISOLATED SHOWERS
AND UPPER LEVEL CLOUDINESS FROM NEAR THE SURFACE TROUGH TO THE
CAPE VERDE ISLANDS TO THE MAURITANIAN COAST.  THE AFOREMENTIONED
VIGOROUS COLD FRONT WILL REACH THE WESTERN ATLANTIC LATE ON
TUESDAY AND NORTH WINDS WILL IMPACT THE BAHAMAS AND THE ATLANTIC
EASTWARD TO ABOUT 65W ON WEDNESDAY.

$$
CWL

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