[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171733
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST SAT JAN 17 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 6N9W 4N15W 2N21W 1N30W CROSSING
THE EQUATOR NEAR 41W AND EXTENDING INTO NE BRAZIL NEAR 3S51W.
SCATTERED MODERATE CONVECTION IS FROM 3N-7N BETWEEN 10W-13W.
NUMEROUS MODERATE CONVECTION IS FROM 1N-4N BETWEEN 14W-29W.
SCATTERED MODERATE CONVECTION IS S OF 5N BETWEEN 31W-42W.

...DISCUSSION...

THE GULF OF MEXICO...
A RELATIVELY COOL AND DRY AIRMASS IS IN PLACE ACROSS THE GULF
REGION. THIS AIRMASS IS BEING SUPPORTED BY A 1035 MB SURFACE
HIGH CENTERED OVER E ALABAMA NEAR 32N86W...WITH A SURFACE RIDGE
EXTENDING SOUTHWESTWARD FROM THIS SURFACE HIGH ACROSS THE GULF
REGION. SUBSIDENCE ASSOCIATED WITH THE SURFACE HIGH AND SURFACE
RIDGE ARE RESULTING IN GENERALLY FAIR WEATHER ACROSS THE GULF
REGION. AT THE SAME TIME...A BROAD UPPER LEVEL TROUGH COVERS THE
GULF REGION...WITH NORTHWESTERLY FLOW ALOFT ENHANCING THE
SUBSIDENCE ACROSS THE W GULF. DEEP LAYER DRY AIR IS PRESENT
ACROSS THE N GULF...WHILE MID/UPPER-LEVEL MOISTURE IS STREAMING
EASTWARD ACROSS THE S GULF. THE AFOREMENTIONED SURFACE HIGH AND
SURFACE RIDGE ARE FORECAST TO MOVE EASTWARD DURING THE NEXT TWO
DAYS...ALLOWING A SURFACE COLD FRONT TO MOVE SOUTHWARD ACROSS
THE N AND W GULF FOR SUNDAY THROUGH MONDAY. ADDITIONALLY...
STRONG N TO NE SURFACE WINDS ARE BLOWING THROUGH THE ISTHMUS OF
TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE E PACIFIC
REGION. THESE WINDS ARE FORECAST TO HAVE DIMINISHED BELOW GALE
FORCE AT 18/1200 UTC.

THE CARIBBEAN SEA...
ACROSS THE W CARIBBEAN...A DISSIPATING SURFACE STATIONARY FRONT
EXTENDS FROM CENTRAL CUBA NEAR 22N78W TO 18N84W TO N OF HONDURAS
NEAR 16N86W. RELATIVELY COOLER AND DRIER CONDITIONS ARE PRESENT
TO THE NW OF THIS FRONT. LOW LEVEL CONVERGENCE IS SUPPORTING
SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS FRONT. THIS
ACTIVITY IS BEING ENHANCED BY ATMOSPHERIC LIFT IN MOIST
SOUTHWESTERLY FLOW ALOFT PRESENT ACROSS THE W CARIBBEAN. ACROSS
THE E CARIBBEAN...AN UPPER LEVEL RIDGE IS PRESENT AND IS
ASSOCIATED WITH SUBSIDENCE...DEEP LAYER DRY AIR...AND STABLE
ATMOSPHERIC CONDITIONS. AS A RESULT...GENERALLY FAIR WEATHER
PERSISTS ACROSS THE E CARIBBEAN. HOWEVER...A SURFACE TROUGH
ENTERS THE E CARIBBEAN FROM THE SW N ATLC AND EXTENDS FROM
PUERTO RICO NEAR 18N66W TO 15N67W TO 12N67W. SURFACE
OBSERVATIONS INDICATE A REGION OF CYCLONIC CURVATURE IN THE
SURFACE WIND FIELD IN THE VICINITY OF THIS SURFACE TROUGH...
WHERE VISIBLE SATELLITE IMAGERY DEPICTS CYCLONIC MOTION OF LOW
LEVEL CLOUDS. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED
SHOWERS WITHIN 90 NM EITHER SIDE OF THIS SURFACE TROUGH N OF 14N.

THE ATLANTIC OCEAN...
STRONG SOUTHWESTERLY FLOW ALOFT IS PRESENT ACROSS THE W ATLC...
WITH A DEEP TROUGH OVER THE E CONUS AND W ATLC. THE DEEP TROUGH
IS ASSOCIATED WITH A SURFACE STATIONARY FRONT THAT EXTENDS FROM
CENTRAL CUBA NEAR 22N78W TO 27N67W TO 32N59W TO NE OF THE
DISCUSSION AREA. THIS STATIONARY FRONT IS DISSIPATING E OF 61W
AND W OF 76W. THE DEEP TROUGH IS ALSO ASSOCIATED WITH A SURFACE
COLD FRONT THAT EXTENDS FROM 31N70W TO 32N67W TO NE OF THE
DISCUSSION AREA. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED
SHOWERS WITHIN 60 NM EITHER SIDE OF THE STATIONARY FRONT AND
COLD FRONT. ADDITIONALLY...A STRONG SURFACE COLD FRONT IS
FORECAST MOVE OFF THE SE UNITED STATES COAST SUNDAY NIGHT AND
MOVE ACROSS PORTIONS OF THE SW N ATLC SUNDAY NIGHT THROUGH
TUESDAY...WITH GALE CONDITIONS EXPECTED ACROSS PORTIONS OF THE
SW N ATLC ON MONDAY. FARTHER TO THE E...A SURFACE TROUGH EXTENDS
FROM 22N65W TO 20N66W TO PUERTO RICO NEAR 18N66W AND EXTENDS
INTO THE E CARIBBEAN REGION. SURFACE OBSERVATIONS AND VISIBLE
SATELLITE INDICATE THE PRESENCE OF THIS SURFACE TROUGH...AND LOW
LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 90 NM
EITHER SIDE OF THIS SURFACE TROUGH. FARTHER TO THE E...AN UPPER
HIGH IS CENTERED NEAR 29N39W...WITH A 1035 MB SURFACE HIGH
CENTERED NEAR 32N34W. SUBSIDENCE AND STABLE ATMOSPHERIC
CONDITIONS ASSOCIATED WITH THE UPPER HIGH AND SURFACE HIGH ARE
RESULTING IN GENERALLY FAIR WEATHER ACROSS MUCH OF THE CENTRAL
AND E ATLC. ACROSS THE TROPICAL ATLC...WESTERLY FLOW ALOFT IS
PRESENT...WITH UPPER LEVEL DIFFLUENCE ENHANCING THE CONVECTION
ASSOCIATED WITH THE ITCZ.

$$
COHEN




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