[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181757
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU SEP 18 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1645 UTC.

...TROPICAL WAVES...
TROPICAL WAVE IS OVER THE CAPE VERDE ISLANDS ALONG 24W/25W S OF
17N MOVING W NEAR 10 KT. A LOW/MID LEVEL LOW IS OVER THE CAPE
VERDE ISLANDS WITH THE WAVE EMBEDDED WITHIN AN AREA OF DEEP
LAYERED MOISTURE AS INDICATED BY THE MIMIC TPW ANIMATION.
HOWEVER...THE AREA LACKS ANY ASSOCIATED DEEP CONVECTION OR
SHOWERS.

TROPICAL WAVE IS ALONG 44W/45W S OF 19N MOVING WNW NEAR 10 KT.
MID LEVEL LOW IS ALONG THE WAVE AXIS NEAR 17N. THIS WAVE IS
EMBEDDED WITHIN AN AREA OF DRY SOMEWHAT STABLE AIR...THUS NO
ASSOCIATED SHOWERS/CONVECTION.

TROPICAL WAVE AS ADDED TO THE 1200 UTC ANALYSIS BASED ON A
LONG-TERM SATELLITE LOOP ALONG 62W S OF 20N MOVING W NEAR 10 KT.
AN UPPER TROUGH IS TO THE W OF THE WAVE AND AN UPPER RIDGE TO
THE E IS GREATLY ENHANCING THE ACTIVITY ASSOCIATED WITH THIS
WAVE. BROAD AREA OF SCATTERED MODERATE TO SCATTERED STRONG
CONVECTION COVERS THE AREA FROM 12N-19N BETWEEN 57W-64W
INCLUDING THE LESSER ANTILLES.

TROPICAL WAVE IS ALONG 71W/72W S OF 19N MOVING W NEAR 15 KT. AN
UPPER RIDGE IS JUST TO THE W OF THE WAVE AXIS ENHANCING
CONVECTION ASSOCIATED WITH THIS WAVE. CLUSTERS OF SCATTERED
MODERATE TO ISOLATED STRONG CONVECTION ARE OVER THE CENTRAL
CARIBBEAN FROM 11N-18N BETWEEN 70W-77W.

TROPICAL WAVE IS ALONG 88W S OF 22N MOVING W 10-15 KT. WAVE IS
ALONG THE COAST OF YUCATAN PENINSULA WITH ANY ASSOCIATED
CONVECTION INLAND OVER CENTRAL AMERICA AND THE E PACIFIC REGION.

...THE ITCZ...
ITCZ AXIS IS ANALYZED ALONG 16N16W 8N29W 11N48W 13N60W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 150 NM N
OF THE ITCZ FROM 53W-57W AND WITHIN 90/120 NM S OF THE ITCZ FROM
52W-58W. AN UPPER RIDGE COVERS THE LESSER ANTILLES AND FAR E
CARIBBEAN INTO THE W TROPICAL ATLC PROVIDING UPPER LEVEL
DIFFLUENCE ENHANCING THIS CONVECTION.

...DISCUSSION...

GULF OF MEXICO...
A WEAK STATIONARY FRONT EXTENDS FROM NEAR TAMPA FLORIDA TO
27N92.5W. SOUTH OF THIS POINT...A WARM FRONT EXTENDS S TO 1012
MB LOW AT 21.5N96W...WITH A STATIONARY FRONT STRETCHING SE FROM
THE LOW TO 18.5N94.5W. THESE FEATURES ARE RESULTING IN SCATTERED
SHOWERS AND THUNDERSTORMS OVER THE W GULF S OF THE FRONT TO 90W.
AN UPPER LEVEL TROUGH ASSOCIATED WITH THE FRONT IS SLIPPING S
ACROSS THE NE GULF...WITH DRY AIR DROPPING S TO NEAR TAMPA
FLORIDA E OF 88W. INSTABILITY NEAR THE TROUGH AXIS IS PRODUCING
ISOLATED SHOWERS AND THUNDERSTORMS OVER THE FAR NE GULF. AN
UPPER LEVEL RIDGE EXTENDING FROM AN UPPER HIGH NEAR 20.5N97W
COVERS THE S GULF. UPPER LEVEL DIFFLUENCE E OF THE HIGH IS
FURTHER AIDING SCATTERED MODERATE CONVECTION IN THE BAY OF
CAMPECHE. ACROSS THE SE GULF...MAINLY FAIR WEATHER UNDER THE
INFLUENCE OF CONFLUENT NORTHWESTERLY FLOW ALOFT. THE SURFACE LOW
IS EXPECTED TO DRIFT NORTHWARD AS THE FRONT BEGINS TO DISSIPATE
INTO THE WEEKEND.

CARIBBEAN SEA...
TWO TROPICAL WAVES ARE OVER THE CARIBBEAN SEA AND CENTRAL
AMERICA. SEE ABOVE. DIFFLUENCE IN NORTHERLY FLOW ALOFT IN THE S
CARIBBEAN IS GENERATING SEVERAL CLUSTERS OF MODERATE WITH
ISOLATED STRONG CONVECTION S OF 17N W OF 77W TO INLAND OVER
CENTRAL AMERICA. A WEAK 1010 MB LOW HAS FORMED OVER PANAMA NEAR
9.5N79.5W...WHICH IS FURTHER AIDING THE CONVECTION NEAR PANAMA.
FURTHERMORE...AN UPPER LEVEL TROUGH EXTENDS FROM AN UPPER LOW
OVER PUERTO RICO TO VENEZUELA NEAR THE ABC ISLANDS AND IS
ENHANCING CONVECTION ASSOCIATED WITH THE TROPICAL WAVE ALONG
62W...AFFECTING MUCH OF THE LESSER ANTILLES. AN UPPER RIDGE
COVERS THE FAR E CARIBBEAN INTO THE W ATLC ANCHORED NEAR
TRINIDAD. MOSTLY FAIR WEATHER IS OCCURRING ACROSS THE NORTHWEST
CARIBBEAN WHERE DRY AIR IN NORTHERLY FLOW ALOFT PREDOMINATES.

ATLANTIC OCEAN...
TWO TROPICAL WAVES ARE OVER THE ATLANTIC OCEAN WITH NO
ASSOCIATED CONVECTION. SEE ABOVE. A COLD FRONT EXTENDS SW FROM A
1014 MB LOW NEAR 32.5N74W ACROSS FLORIDA NEAR MELBOURNE INTO THE
GULF AS STATIONARY BOUNDARY. A WEAK SURFACE TROUGH EXTENDS FROM
30.5N69W TO 25.5N73.5W. THESE FEATURES ARE RESULTING IN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE W ATLC...
W OF LINE FROM 30N68W TO THE N CUBA COAST NEAR 21N77W INCLUDING
THE N BAHAMA ISLANDS AND THE FLORIDA PENINSULA. MOIST
SOUTHWESTERLY FLOW ALOFT AHEAD OF AN UPPER LEVEL TROUGH
ASSOCIATED WITH THE FRONT IS OVER THE E CONUS COAST AND IS
FURTHER AIDING THIS ACTIVITY. A SURFACE RIDGE EXTENDING
SOUTHWESTWARD FROM A 1023 MB HIGH IN THE N/CENTRAL ATLC IS
BRINGING FAIR WEATHER TO MUCH OF THE AREA. AN UPPER LEVEL LOW
NEAR 22.5N41.5W AND ASSOCIATED SURFACE TROUGH FROM 32N40W TO
29N42.5W TO 27N47W ARE GENERATING CLOUDINESS OVER PORTIONS OF
THE CENTRAL ATLANTIC WITH POSSIBLE ISOLATED SHOWERS. AN UPPER
LEVEL TROUGH OVER THE NE ATLC IS GENERATING CLOUDS AND SCATTERED
SHOWERS N OF 27N AND E OF 20W TO OVER THE CANARY ISLANDS. THE
TYPICAL LARGE E/W UPPER LEVEL RIDGE IS ACROSS THE REMAINDER OF
THE TROPICAL ATLC BRINGING FAIR WEATHER TO THE CENTRAL AND E
TROPICAL ATLC.

$$
COHEN/WALLACE

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