[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 122343
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST FRI DEC 12 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...THE ITCZ...
THE ITCZ IS CENTERED ALONG 8N13W 4N30W 4N45W 5N54W. A SURFACE
TROUGH IS EMBEDDED WITHIN THE ITCZ. ITS AXIS EXTENDS ALONG
55W/56W SOUTH OF 14W. CONVECTION ASSOCIATED WITH THIS FEATURE
HAS DIMINISHED SINCE YESTERDAY. A SWIRL OF LOW CLOUDS IS ALONG
THE TROUGH AXIS NEAR 10N. ISOLATED MODERATE CONVECTION IS FROM
6N-10N BETWEEN 50W-56W. ELSEWHERE...SCATTERED MODERATE
CONVECTION IS WITHIN 100 NM NE OF LINE 5N30W 7N38W 9N42W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS INLAND OVER SW
AFRICA FROM 4N-8N BETWEEN THE PRIME MERIDIAN AND 10W.

...DISCUSSION...

GULF OF MEXICO...
A RELATIVELY COOLER AND DRIER AIRMASS IS PRESENT ACROSS THE GULF
REGION IN THE WAKE OF A SURFACE COLD FRONT THAT EXTENDS FROM THE
W ATLC INTO THE W CARIBBEAN. THIS AIRMASS IS BEING REINFORCED BY
A SECONDARY COLD FRONT THAT LIES ACROSS SOUTH FLORIDA AND THE SE
PORTION OF THE GULF TO NEAR 22N88W. THE INCREASED SURFACE
PRESSURE GRADIENT IN THE VICINITY OF THIS SECONDARY COLD FRONT
IS SUPPORTING NORTHERLY SURFACE WINDS OF 20 TO 25 KT ACROSS
PORTIONS OF THE MIDDLE AND E GULF. BROKEN TO OVERCAST
STRATOCUMULUS CLOUDS COVER THE SOUTHERN HALF OF THE GULF
INCLUDING ALSO THE BAY OF CAMPECHE AND THE YUCATAN PENINSULA DUE
TO THE COLD AIR ADVECTION OVER RELATIVELY WARM WATERS. MODERATE
TO STRONG SUBSIDENCE IN STRONG WESTERLY AND NORTHWESTERLY FLOW
ALOFT IS INHIBITING DEEP CONVECTION ACROSS THE GULF REGION. THIS
SUBSIDENCE IS BEING ENHANCED OVER THE W GULF...WHERE A SURFACE
RIDGE DOMINATES. THIS RIDGE IS BEING ANCHORED BY A 1028 MB
SURFACE HIGH LOCATED OVER THE UPPER TEXAS COAST. ADDITIONALLY...
STRONG N TO NE SURFACE WINDS ARE BLOWING THROUGH THE ISTHMUS OF
TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE E PACIFIC
REGION. LOOKING AHEAD...THE RETURN FLOW IS EXPECTED TO INCREASE
SAT THROUGH LATE SUN AS LOW PRES MOVES THROUGH CENTRAL PLAINS.

CARIBBEAN SEA...
THE COLD FRONT OVER THE W ATLC ENTERS THE CARIBBEAN SEA THROUGH
EASTERN CUBA THEN CONTINUES MAINLY SOUTH AS A STATIONARY FRONT
TO COSTA RICA NEAR 10N83W. SCATTERED SHOWERS ARE ALONG AND
WITHIN 60 NM EITHER SIDE OF THIS FRONT. BEHIND THE FRONT...A
RELATIVELY COOLER AND DRIER AIRMASS HAS INVADED THE NW CARIBBEAN
INCLUDING ALSO WEST AND CENTRAL CUBA AND NORTHERN CENTRAL
AMERICA WHERE BROKEN TO OVERCAST LOW TO MID CLOUDS WITH EMBEDDED
LIGHT SHOWERS ARE NOTED. IN ADDITION...NLY WINDS OF 20 TO 30 KT
ARE BLOWING W OF THE FRONT WITH THE STRONGEST WINDS NEAR THE
COAST OF NICARAGUA. THE REMAINDER OF THE CARIBBEAN SEA REMAINS
UNDER THE INFLUENCE OF A STRONG HIGH PRES SYSTEM...ANALYZED 1040
MB...NEAR THE AZORES. PATCHES OF LOW LEVEL MOISTURE CARRIED BY
THE TRADE WINDS CONTINUE TO MOVE EWD AROUND THE PERIPHERY OF
THIS SFC HIGH WHICH IS ALSO PRODUCING A WIDE SWATH OF MODERATE
TO STRONG ELY WINDS ACROSS THE ATLANTIC OCEAN AND THE E-CENTRAL
CARIBBEAN. SATELLITE IMAGERY REVEALS AN AREA OF LOW TOPPED
SHOWERS JUST SOUTH OF JAMAICA MOVING W-SW AHEAD OF THE
STATIONARY FRONT. ALOFT...A RIDGE EXTENDS FROM N COLOMBIA TO
GUATEMALA AND SE MEXICO. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH
THIS UPPER RIDGE COMBINED WITH THE TAIL END OF THE ABOVE
MENTIONED FRONT AND THE COLOMBIAN LOW IS HELPING TO INDUCE
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE SW
CARIBBEAN INCLUDING ALSO COSTA RICA AND PANAMA.

ATLANTIC OCEAN...
A DEEP LAYERED TROUGH OVER THE EASTERN CONUS SUPPORTS A PAIR OF
COLD FRONTS OVER THE W ATLC. THE MAIN ONE ENTERS THE FORECAST
AREA NEAR 31N72W THE CONTINUES SW OVER THE CENTRAL BAHAMAS AND
EASTERN CUBA WHERE IT BECOMES STATIONARY CONTINUING OVER THE
CARIBBEAN SEA. THE SECONDARY FRONT CROSSES THE NW BAHAMAS...
SOUTH FLORIDA AND THE SE PORTION OF THE GULF OF MEXICO. MUCH
DRIER AND COOLER AIR WILL MOVE OVER SOUTH FLORIDA TONIGHT BEHIND
THIS REINFORCING COLD FRONT. A PRE-FRONTAL TROUGH WITH A BAND OF
SCATTERED SHOWERS AND ISOLATED TSTMS IS WITHIN AROUND 70 NM E OF
THE LEAD FRONT N OF THE BAHAMAS. NWLY WINDS OF 20 TO 30 KT AND
COLD AIR STRATOCUMULUS CLOUDS FOLLOW THE FRONTS. THE REMAINDER
OF THE DISCUSSION AREA IS UNDER THE INFLUENCE OF A STRONG SFC
HIGH PRES SYSTEM FORECAST TO REMAIN STATIONARY DURING THE NEXT
24 HOURS. SUBSIDENCE AROUND THIS 1040 MB SURFACE HIGH CENTERED
NEAR THE AZORES IS GENERALLY SUPPORTING FAIR WEATHER CONDITIONS
ACROSS MUCH OF THE E-CENTRAL ATLC. HOWEVER...AN UPPER-LEVEL LOW
CENTERED NEAR 28N55W IS PRODUCING SCATTERED SHOWERS WITHIN 180
NM NE OF LINE 21N48W 28N57W. THIS SFC HIGH IS ALSO GENERATING A
WIDE SWATH OF MODERATE TO STRONG ELY WINDS ACROSS THE OCEAN
PARTICULARLY FROM 22N-30N EAST OF 55W.  AN UPPER-LEVEL TROUGH
EXTENDS SWD FROM THE ABOVE MENTIONED UPPER-LEVEL LOW INTO THE
DEEP TROPICS ALONG 55W. A JET-STREAM BRANCH WITH CORE WINDS OF
70-90 KT ROUNDS THE BASE OF THIS TROUGH THEN CONTINUES MAINLY
EWD CROSSING N OF THE CAPE VERDE ISLANDS AND ENTERING WEST
AFRICA NEAR 20N17W. EARLY NEXT WEEK...COMPUTER MODELS HAVE COME
INTO MUCH BETTER AGREEMENT ANTICIPATING THE DEVELOPMENT OF A
DEEP LOW PRES SYSTEM OVER THE TROPICAL CENTRAL ATLC. THIS LOW
MAY BE ASSOCIATED WITH THE SURFACE TROUGH THAT HAS BEEN NEARLY
STATIONARY E OF THE LESSER ANTILLES DURING THE PREVIOUS DAYS.

$$
GR









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