[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 112356
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT OCT 11 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.

...SPECIAL FEATURES...
A 1008 MB SURFACE LOW IS NEAR 14N36W...WITH SCATTERED MODERATE
CONVECTION WITHIN 360 NM OF THE LOW. SATELLITE IMAGERY AND
COMPUTER MODEL GUIDANCE DEPICT A BROAD AREA OF LOW LEVEL
CIRCULATION AND CONVERGENCE IN THE VICINITY OF THIS LOW AND THE
TROPICAL WAVE TO ITS WEST. AS A RESULT...A LARGE AREA OF
DISTURBED WEATHER IS OCCURRING AROUND 1390 NM E OF THE LESSER
ANTILLES...MOVING N 5-10 KT. A TROPICAL DEPRESSION COULD FORM IN
THIS AREA DURING THE NEXT DAY OR SO.

...TROPICAL WAVES...
THE TROPICAL WAVE THAT WAS PREVIOUSLY ALONG 37W S OF 17N AT
1200 UTC ON 11 OCT 2008 IS REPOSITIONED FURTHER TO THE W. AT
1800 UTC ON 11 OCT 2008...THIS WAVE IS TILTED FROM NW TO SE FROM
19N40W TO 9N38W MOVING W NEAR 10 KT. THIS WAVE HAS NOW PUSHED TO
THE W OF THE 1008 MB SURFACE LOW NEAR 14N36W. THIS IS EVIDENT IN
VISIBLE SATELLITE IMAGERY...WHICH DEPICTS A SUBTLE INVERTED-V
LOW LEVEL CLOUD PATTERN AND WEAK LOW LEVEL CIRCULATION MOVING
W OF THE LOW. STRONGER EASTERLY LOW LEVEL FLOW N OF THE SURFACE
LOW IS CONTRIBUTING TO THE NW-SE TILT.

A TROPICAL WAVE IS ALONG 52W FROM 14N-22N MOVING W 10-15 KT.
CIMSS WAVETRAK PRODUCT SHOWS SOME WEAK LOW LEVEL CIRCULATION
NEAR THE WAVE AXIS. OTHERWISE...WAVE IS RATHER ILL-DEFINED.
ISOLATED SHOWERS ARE WITHIN 60 NM E OF THE WAVE AXIS N OF 19N.

THE TROPICAL WAVE THAT WAS PREVIOUSLY ALONG 63W S OF 19N AT
1200 UTC ON 11 OCT 2008 IS REPOSITIONED FURTHER TO THE W. AT
1800 UTC ON 11 OCT 2008...THIS WAVE IS ALONG 65W S OF 19N MOVING
W NEAR 10 KT. THIS WAVE HAS PUSHED TO THE W OF A 1008 MB SURFACE
LOW LOCATED IN THE E CARIBBEAN NEAR 13N63W. SURFACE OBSERVATIONS
AND A RECENT ASCAT PASS DEPICT COUNTERCLOCKWISE CURVATURE IN THE
SURFACE FLOW ALONG WAVE AXIS. ISOLATED MODERATE CONVECTION IS
WITHIN 120 NM E OF THE WAVE AXIS AND IS BEING ENHANCED BY A
1008 MB SURFACE LOW NEAR 13N63W.

A TROPICAL WAVE IS OVER N CENTRAL AMERICA AND THE E PACIFIC
ALONG 89W S OF 19N MOVING W NEAR 10 KT. A MAXIMUM IN DEEP LAYER
MOISTURE COINCIDES WITH THE WAVE AXIS BASED ON CIMSS TOTAL
PRECIPITABLE WATER PRODUCT. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS WITHIN 210 NM OF WAVE AXIS N OF 11N...AFFECTING
THE YUCATAN PENINSULA...AS WELL AS NICARAGUA AND COSTA RICA.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 7N13W 8N27W 11N35W 8N47W 10N61W. IN
ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...
ISOLATED MODERATE CONVECTION IS FROM 2N-9N BETWEEN 22W-31W.
SIMILAR CONVECTION IS FROM 8N-11N BETWEEN 41W-44W. SCATTERED
MODERATE CONVECTION IS FROM 6N-11N BETWEEN 58W-69W...AFFECTING N
VENEZUELA AND N GUYANA.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER HIGH IS CENTERED OVER S TEXAS NEAR 26N97W...WITH DRY
NORTHERLY UPPER FLOW FLOW EAST OF THIS HIGH OVER MUCH OF THE
GULF. A SHARP UPPER TROUGH EXTENDS FROM FL TO CENTRAL CUBA AND
THE NW CARIBBEAN. AN ASSOCIATED WEAK SURFACE TROUGH EXTENDS FROM
THE S FLORIDA PENINSULA NEAR 25N80W TO THE FLORIDA KEYS NEAR
24N81W. WEAK LOW LEVEL CONVERGENCE AND ENHANCED INSTABILITY
UNDER THE UPPER TROUGH ARE RESULTING IN SCATTERED SHOWERS AND
THUNDERSTORMS OVER S FLORIDA...THE FLORIDA KEYS...W CUBA...AND
THE ADJACENT GULF WATERS. ALSO...A WEAK SURFACE TROUGH IS OVER
THE W GULF EXTENDING FROM 24N96W TO 21N95W TO 19N93W...AND IS
RESULTING IN SCATTERED MODERATE CONVECTION WITHIN 120 NM W OF
THE TROUGH AXIS N OF 22N. THE TROPICAL WAVE ALONG 89W IS
ENHANCING SCATTERED MODERATE/ISOLATED STRONG CONVECTION OVER THE
W YUCATAN PENINSULA...WHICH IS IMPACTING THE ADJACENT GULF
WATERS. OTHERWISE...A SURFACE RIDGE EXTENDS FROM THE E CONUS
INTO THE CENTRAL AND N GULF...RESULTING IN FAIR WEATHER ACROSS
MUCH OF THE CENTRAL AND NW GULF...WITH MOSTLY E AND NE SURFACE
WINDS PREVAILING.

CARIBBEAN SEA...
A 1008 MB SURFACE LOW IS LOCATED IN THE SE CARIBBEAN NEAR
13N63W...AND IS SUPPORTING SCATTERED MODERATE CONVECTION FROM
10N-16N BETWEEN 56W-64W...AFFECTING THE LESSER ANTILLES. THIS
CONVECTION IS BEING ENHANCED BY DEEP MOISTURE IN SW FLOW ALOFT
SE OF AN UPPER LOW NEAR 20N66W. THERE IS THE POTENTIAL FOR
ADDITIONAL SLOW DEVELOPMENT OF THIS SYSTEM DURING THE NEXT DAY
OR TWO AS THE SYSTEM MOVES SLOWLY TO THE NW. ANOTHER 1008 MB
SURFACE LOW IS CENTERED IN THE SW CARIBBEAN NEAR 11N81W...AND IS
GENERATING SCATTERED MODERATE CONVECTION WITHIN 180 NM OF THE
CENTER... AFFECTING NICARAGUA AND COSTA RICA. THIS CONVECTION IS
FURTHER BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN NW FLOW
ALOFT SW OF AN UPPER TROUGH THAT EXTENDS FROM CENTRAL CUBA TO
PANAMA. DRY AIR AND A WEAK UPPER RIDGE OVER THE CENTRAL
CARIBBEAN ARE RESULTING IN GENERALLY FAIR WEATHER THERE.
SCATTERED MODERATE CONVECTION THAT DEVELOPED OVER THE HIGHER
TERRAIN OF HISPANIOLA...N COLOMBIA...AND N VENEZUELA EARLIER
THIS AFTERNOON IS IMPACTING THE NEARBY CARIBBEAN WATERS.

ATLANTIC OCEAN...
OVER THE TROPICAL ATLC...A 1008 MB SURFACE LOW IS NEAR 14N36W.
PLEASE SEE SPECIAL FEATURES SECTION ABOVE FOR MORE INFORMATION
ON THIS FEATURE. INSTABILITY BENEATH AN UPPER TROUGH OVER THE W
ATLC IS SUPPORTING ISOLATED SHOWERS AND THUNDERSTORMS FROM
25N-32N W OF 74W...AFFECTING THE BAHAMAS AND THE E FLORIDA
PENINSULA. A SURFACE TROUGH EXTENDS FROM 32N77W TO 28N78W TO
S FLORIDA NEAR 25N80W AND IS FURTHER ENHANCING THIS ACTIVITY. TO
THE E...AN UPPER HIGH IS CENTERED OVER THE SW ATLC NEAR
23N70W...WITH SUBSIDENCE AND DEEP DRY LAYER AIR NEAR THE HIGH.
TO THE NE...A SURFACE TROUGH EXTENDS FROM 28N67W TO 25N68W TO
22N68W. ISOLATED MODERATE CONVECTION IS WITHIN 60 NM W OF THE
TROUGH N OF 24N AND SCATTERED MODERATE CONVECTION WITHIN 180 NM
E OF THE TROUGH N OF 24N. TO THE E OF THIS SURFACE TROUGH...AN
UPPER TROUGH AXIS EXTENDS ACROSS THE CENTRAL ATLC FROM 32N47W TO
24N53W TO 23N63W TO AN UPPER LOW JUST N OF PUERTO RICO NEAR
20N67W. THIS UPPER TROUGH IS RELATIVELY DEEPER N OF 27N AND IS
ASSOCIATED WITH A WEAKENING SURFACE STATIONARY FRONT THAT
EXTENDS FROM 32N46W TO 29N50W TO 27N53W. DRY AIR EMBEDDED WITHIN
THE UPPER TROUGH IS INHIBITING ANY CONVECTION WITH THE FRONT. TO
THE E OF THIS FRONT...A SURFACE TROUGH EXTENDS FROM 31N45W TO
28N46W TO 25N47W. MOIST SOUTHWESTERLY FLOW ALOFT E OF THE UPPER
TROUGH IS SUPPORTING SCATTERED MODERATE CONVECTION WITHIN 120 NM
EITHER SIDE OF THE SURFACE TROUGH. FURTHER TO THE E...AN UPPER
RIDGE IS N OF 19N BETWEEN 34W-44W...AN UPPER LOW IS NEAR
27N29W...AND A SURFACE TROUGH EXTENDS TO THE SW OF A 1010 MB LOW
NEAR 31N12W TO NW AFRICA NEAR 26N14W TO 21N18W. DEEP LAYER DRY
IS IN INHIBITING ANY CONVECTION WITH THESE FEATURES. OVER THE
TROPICAL ATLC...AN UPPER RIDGE EXTENDS ALONG 10N BETWEEN AFRICA
AND NEAR 47W.

$$
COHEN



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