[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 212350
TWDAT

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

...THE ITCZ...
THE ITCZ IS PRETTY ACTIVE THIS EVENING. IT AXIS IS CENTERED
ALONG 5N10W 5N20W 4N30W 3N40W AND INTO SOUTH AMERICA NEAR THE
EQUATOR AT 50W. CLUSTERS OF MODERATE TO STRONG CONVECTION ARE
FROM THE EQUATOR TO 6N BETWEEN 30W-40W...AND WITHIN 90 NM SOUTH
OF AXIS BETWEEN 20W-29W. UPPER DIFFLUENCE IS ENHANCING
CONVECTION ALONG THE ITCZ.

DISCUSSION...
GULF OF MEXICO...
AS WAS PREDICTED BY THE COMPUTER MODELS...A SFC LOW DEVELOPED
AND MOVED QUICKLY ACROSS THE NE QUADRANT OF THE GULF AND N
FLORIDA 24 HOURS AGO...AND NOW IS CENTERED NEAR 31N79W. A COLD
FRONT EXTENDS FROM THIS LOW ACROSS SOUTH FLORIDA AND THE GULF
ALONG 25N85W 24N90W CURVING AS A STATIONARY FRONT INTO THE SW
PORTION OF THE GULF. A RATHER SHARP WIND SHIFT IS ASSOCIATED
WITH THE FRONT WITH SW WINDS OF 15 KT AHEAD OF THE FRONT AND NW
TO N WINDS OF 10-15 KT W OF THE FRONT TO ABOUT 90W. THE FRONT IS
FORECAST TO EXIT THE AREA TONIGHT AND A WEAK HIGH PRES WILL
BUILD IN. A RETURN FLOW IS ALREADY ESTABLISHED OVER THE FAR W
GULF IN ADVANCE OF A STRONGER COLD FRONT THAT WILL MOVE OFF THE
TEXAS COAST SAT AFTERNOON. MODERATE TO STRONG NLY WINDS OF 25 TO
30 KT AND BUILDING SEAS CAN BE EXPECTED BEHIND FRONT. ALOFT...A
RIDGE DOMINATES THE ENTIRE GULF WHILE A MID/UPPER LEVEL TROUGH
IS LOCATED JUST EAST OF THE FLORIDA PENINSULA. THIS TROUGH
SUPPORTS THE ABOVE MENTIONED LOW/FRONT. MODERATE TO STRONG
SUBSIDENCE COVERS THE GULF EXCEPT THE NW CORNER WHERE A
SUBTROPICAL JETSTREAM FROM THE EPAC IS ADVECTING ABUNDANT
UPPER-LEVEL MOISTURE/HIGH CLOUDS.

CARIBBEAN SEA...
TRANQUIL WEATHER CONDITIONS PERSIST ACROSS MOST OF THE CARIBBEAN
SEA THIS EVENING UNDER THE INFLUENCE OF A MID/UPPER-LEVEL RIDGE
WHICH IS PRODUCING STRONG SUBSIDENCE AND A DRY/STABLE AIRMASS.
A SFC TROUGH IS ALONG 63W SOUTH OF 16N GENERATING SOME SHOWER
ACTIVITY OVER THE WINDWARD ISLANDS AND NE VENEZUELA. THE TRADE
WINDS ARE ADVECTING SOME LOW LEVEL MOISTURE ACROSS NICARAGUA...
COSTA RICA AND WESTERN PANAMA. A FEW PATCHES OF LOW LEVEL CLOUDS
WITH ISOLATED SHOWERS ARE OVER THE REMAINDER OF THE BASIN.
LIGHT TO MODERATE TRADES WILL PREVAIL OVER MUCH OF THE AREA
THROUGH MONDAY.

ATLANTIC OCEAN...
MAIN FEATURE ACROSS THE FORECAST AREA IS THE 1006 MB LOW PRES
LOCATED NEAR 31N79W WITH A COLD FRONT EXTENDING SW ACROSS THE NW
BAHAMAS AND SOUTH FLORIDA INTO THE GULF OF MEXICO. MOST OF THE
CONVECTIVE ACTIVITY ASSOCIATED WITH THIS SYSTEM IS WITHIN 140 NM
AHEAD OF THE FRONT. LIGHTNING DATA REVEALS SCATTERED TSTMS
EMBEDDED IN THIS AREA N OF 26N BETWEEN 70W-75W. A QUIKSCAT PASS
FROM THIS MORNING SHOWED 20-30 KT WINDS NEAR THE LOW AND JUST N
OF 31N W OF 70W WHERE GALE FORCE WINDS ARE OCCURRING. ACCORDING
TO THE GFS COMPUTER MODEL...THE LOW WILL MOVE SE AND WEAKEN
TONIGHT REACHING TO NEAR 29N70W BY SAT MORNING. A RIDGE WILL
BUILD BEHIND THE LOW BETWEEN THE SE U.S. AND WEST-CENTRAL CUBA.
THE TIGHT PRES GRADIENT BETWEEN THE LOW AND A HIGH SITUATED
NORTH OF THE AREA WILL PRODUCE MODERATE TO STRONG NELY WINDS
ACROSS THE W ATLC DURING THE UPCOMING WEEKEND. FARTHER EAST...A
SFC TROUGH EXTENDS FROM A WEAK 1014 MB LOW LOCATED NEAR 34N46W
TO 24N55W. SCATTERED SHOWERS AND TSTMS ARE WITHIN 125 NM AHEAD
OF THE TROUGH N OF 25N. ANOTHER COLD FRONT ENTERS THE AREA NEAR
31N17W THEN CONTINUES SW AND W ALONG 27N25W TO 31N36W WHERE IT
CONNECTS TO A WARM FRONT. A LARGE SFC RIDGE REMAINS FIXED OVER
THE E ATLC TRANSPORTING FAIR WEATHER STRATOCUMULUS CLOUDS AROUND
ITS PERIPHERY. IN THE TROPICAL ATLC...UPPER DIFFLUENCE IS
SUPPORTING CONVECTION ALONG THE ITCZ.

$$
GR








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