[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 060538
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST SUN DEC 06 2009

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0500 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE AXIS IS CENTERED ALONG 7N12W
6N20W 3N30W 1N40W INTO EXTREME NORTHERN BRAZIL NEAR 1N50W. SCATTERED
MODERATE CONVECTION WITHIN 60 NM N AND 90 NM S OF THE ITCZ AXIS
BETWEEN 16W AND 28W.

...DISCUSSION...

GULF OF MEXICO...
THE 1025 MB HIGH PRES SYSTEM OVER THE LOWER MISSISSIPPI VALLEY WILL
RETREAT NORTHEASTWARD THROUGH THE DAY...DECREASING THE PRES GRADIENT
OVER THE EASTERN GULF. THE STRONG NORTHERLY WINDS BEHIND THE COLD
FRONT THAT PASSED THROUGH THE EASTERN GULF AND FLORIDA TODAY ARE
ALREADY BEGINNING TO DIMINISH AS A RESULT. HOWEVER...THE EASTERN
GULF IF STILL MARKED BY STRONG SUBSIDENCE BEHIND THE FRONT. OVER THE
WESTERN GULF...WINDS HAVE ALREADY BEGUN TO TURN EASTERLY TO
SOUTHEASTERLY ON THE SW SIDE OF THIS HIGH PRES CENTER. THESE
SOUTHERLY WINDS ARE FOUND WELL INTO THE SOUTHERN PLAINS AND ARE
FEEDING INTO A LOW PRES SYSTEM CURRENTLY TRAVERSING THE ROCKIES.
SATELLITE-BASED TOTAL PRECIPITABLE WATER IMAGERY REVEALS THAT THIS
SOUTHERLY RETURN FLOW IS ALREADY INCREASING THE AVAILABLE
MOISTURE IN THE WESTERN GULF. INFRARED IMAGERY AND RADAR CONFIRMS
SOME SHOWER ACTIVITY OVER THE SE RIO GRANDE VALLEY AT THE MOMENT.
SHOWER ACTIVITY IS EXPECTED TO INCREASE OVER THE NW GULF TODAY AND
SHIFT EASTWARD INTO THE CENTRAL GULF MON AS THE LOW PRES SYSTEM IN
THE ROCKIES MOVES EAST AND DRAGS A WEAK SURFACE BOUNDARY WITH IT
INTO THE MISSISSIPPI VALLEY.

CARIBBEAN SEA...
THE TRADE WINDS OVER THE CARIBBEAN HAVE WEAKENED DUE TO THE
SLACKENING PRES GRADIENT BETWEEN CLIMATOLOGICAL LOW PRES OVER
NORTHERN COLOMBIA AND THE RIDGE EXTENDING FROM A 1024 MB HIGH NEAR
32N52N TO THE NW CARIBBEAN NEAR 20N80W. THE 0144 UTC ASCAT CONFIRMS
THIS...WITH 20 TO 25 KT EASTERLY TRADEWINDS NOW CONFINED TO NEAR THE
COAST OF NORTHERN COLOMBIA. THE RIDGE N OF THE AREA HAS SHIFTED
EASTWARD DUE TO THE PROGRESSION OF THE COLD FRONT THAT MOVED THROUGH
FLORIDA SAT AND INTO THE SW N ATLANTIC. THE SOUTHERN EDGE OF THIS
FRONT HAS MOVED INTO THE NW CARIBBEAN...BRINGING SHOWERS NEAR THE
FRONT AND 20 TO 25 KT N WINDS N OF THE FRONT. THE FRONT IS EXPECTED
TO STALL OVER THE NW CARIBBEAN AND DISSIPATE LATER TODAY.
ELSEWHERE...THE CARIBBEAN CONTINUES TO BE MARKED BY STRONG
SUBSIDENCE AND LIMITED MOISTURE...BRINGING TRANQUIL WEATHER TO MUCH
OF THE AREA. SCATTERED SHOWERS ARE PRIMARILY LIMITED TO THE EASTERN
CARIBBEAN E OF 70W AND THE CENTRAL CARIBBEAN N OF 15N BETWEEN 70W
AND 80W AT THIS TIME.

ATLANTIC OCEAN...
A COLD FRONT LIES OVER THE SW N ATLANTIC FROM 31N74W TO 27N78W TO
23N81W. THE 0148 ASCAT PASS SHOWS NW WINDS IN THE 20 TO 25 KT RANGE
N OF THE BAHAMAS AND W OF THE COLD FRONT. SCATTERED SHOWERS AND
THUNDERSTORMS LIE WITHIN 180 NM E OF THE COLD FRONT AT THE MOMENT.
THE DEEP LAYER LOW SUPPORTING THIS FRONTAL BOUNDARY IS LIFTING
NORTHEAST OFF THE NEW ENGLAND COAST THIS MORNING AND THE UPPER LEVEL
TROUGHING OVER THE SW N ATLANTIC WILL QUICKLY BE REPLACED BY
WESTWARD BUILDING RIDGING FROM THE CENTRAL ATLANTIC ACROSS THE
BAHAMAS. AS A RESULT...THE COLD FRONT WILL ADVANCE EASTWARD THROUGH
THE NORTHERN PORTION OF THE FORECAST AREA BUT STALL NEAR THE STRAITS
OF FLORIDA TODAY AND BEGIN LIFTING NORTH AS A WEAK WARM FRONT BY
MON. THE ADVANCING COLD FRONT HAS ALREADY SHIFTED THE SURFACE RIDGE
FARTHER EAST OVER THE PAST 24 HOURS...WITH THE RIDGE NOW EXTENDING
FROM 1024 MB HIGH NEAR 32N52N TO THE NW CARIBBEAN NEAR 20N80W. THIS
RIDGING IS EXPECTED TO WEAKEN FURTHER AS THE ADVANCING PORTION OF
THE COLD FRONT ENCROACHES UPON IT. TO THE WEST OF THIS RIDGE LIES AN
UPPER TROUGH THAT WILL AMPLIFY AND BECOMING MORE POSITIVELY OVER THE
NEXT FEW DAYS. A 100 KT WEST-SOUTHWESTERLY UPPER JET LIES ON THE
LEADING EDGE OF THIS TROUGH AND IS TRANSPORTING TROPICAL MOISTURE
NORTHEASTWARD TOWARD WEST AFRICA...WITH MAINLY CLOUDY SKIES FOUND
ALONG THE ROUTE FROM THE FRENCH GUIANA TO CAPE VERDE ISLANDS AS A
RESULT. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THE REAR RIGHT
QUADRANT OF THIS UPPER JET IS CURRENTLY SUPPORTING SCATTERED
MODERATE SHOWERS AND THUNDERSTORMS ALONG THE ITCZ AXIS BETWEEN 16W
AND 28W.

$$
SCHAUER




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