[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 022358
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED SEP 02 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2330 UTC.

...SPECIAL FEATURES...

AS OF 03/0000 UTC TROPICAL STORM ERIKA IS CENTERED NEAR 15.9N
62.0W OR JUST W OF GUADELOUPE. ERIKA HAS BEEN DRIFTING BETWEEN
THE W AND WSW BUT SHOULD BEGIN TO MOVE WWD NEAR 9 KT. ESTIMATED
CENTRAL PRESSURE IS 1008 MB. ERIKA BARELY REMAINS A TROPICAL
STORM WITH MAXIMUM SUSTAINED WINDS OF 35 KT WITH GUSTS TO 45
KT...AND WILL LIKELY WEAKEN FURTHER TONIGHT. NUMEROUS STRONG
CONVECTION IS FROM 13N-19N BETWEEN 57W-63W ALREADY AFFECTING THE
LESSER ANTILLES. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY
UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC AND THE FULL
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
FOR MORE DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 28W S OF 20N MOVING W NEAR 20 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY. SATELLITE IMAGERY AND
SATELLITE DERIVED WINDS INDICATE LOW-LEVEL CYCLONIC FLOW IN THE
VICINITY OF THE WAVE AXIS. A DRY SAHARAN AIR LAYER ALONG WITH
SAHARAN DUST IS W OF THE WAVE AXIS CONFINING CONVECTION TO THE
SRN PORTION OF THE WAVE AXIS ALONG THE ITCZ FROM 8N-10N BETWEEN
24W-30W.

A TROPICAL WAVE EXTENDS FROM 15N44W TO 7N41W MOVING W NEAR 18
KT.  THIS WAVE REMAINS LOW-AMPLITUDE AND EMBEDDED WITHIN THE
ITCZ. SATELLITE IMAGERY INDICATES AN INVERTED-V STRUCTURE IN THE
LOW-LEVEL CLOUDS. THE WAVE IS EMBEDDED WITHIN A LARGE AREA OF
DRY SAHARAN AIR AND DUST WHICH IS INHIBITING DEEP CONVECTION
NEAR THE WAVE. A SMALL AREA OF SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS E OF THE WAVE AXIS FROM 10N-11N BETWEEN
41W-42W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 11N15W 10N30W 10N40W 8N47W
9N55W. A LARGE CLUSTER OF NUMEROUS STRONG CONVECTION IS AT THE
AFRICAN COAST FROM 11N-17N BETWEEN 10W-18W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 7N-11N BETWEEN
14W-18W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A STATIONARY FRONT IS ANALYZED ACROSS NRN
FLORIDA FROM 29N81W CONTINUING ALONG 29N83W 27N86W BECOMING A
COLD FRONT ALONG 25N87W 25N93W. A PRE-FRONTAL TROUGH IS ANALYZED
AHEAD OF THE FRONT ACROSS S FLORIDA ALONG 28N80W 25N84W 23N89W.
ISOLATED SHOWERS/THUNDERSTORMS ARE WITHIN 200 NM AHEAD OF THE
FRONT AND 75 NM BEHIND THE FRONT. SCATTERED
SHOWERS/THUNDERSTORMS ARE ALSO OVER PORTIONS OF CUBA...S FLORIDA
AND THE ADJACENT WATERS. CLEAR SKIES AND HIGH PRESSURE IS
BUILDING IN BEHIND THE FRONT ACROSS THE NW GULF. THE FRONT IS
SUPPORTED BY AN UPPER LEVEL TROUGH ACROSS THE ERN CONUS
EXTENDING INTO THE GULF TO NEAR 24N90W. AN UPPER LEVEL RIDGE IS
ACROSS THE SW GULF CENTERED OVER MEXICO NEAR 22N104W. UPPER
LEVEL DIFFLUENCE ASSOCIATED WITH THE RIDGE IS SUPPORTING
ISOLATED SHOWERS ACROSS THE SRN BAY OF CAMPECHE S OF 21N W OF
93W. EXPECT THE FRONT TO DRIFT SE BEFORE DISSIPATING THU AND FRI.

CARIBBEAN SEA...
AN UPPER LEVEL LOW IS OVER THE NW CARIBBEAN CENTERED NEAR
20N82W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LOW AND THE
RIDGE OVER THE SW GULF IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN PENINSULA S OF 21N W OF
86W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LOW AND AN UPPER
LEVEL HIGH N OF THE BAHAMAS NEAR 28N71W IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS CUBA N OF 20N BETWEEN
75W-85W....AND OVER ERN JAMAICA FROM 18N-19N BETWEEN 77W-79W.
ELSEWHERE ACROSS THE CARIBBEAN...DRY AIR AND SUBSIDENCE ALOFT
ARE SUPPORTING GENERALLY FAIR WEATHER EXCEPT FOR THE FAR E
CARIBBEAN WHICH IS BEGINNING TO FEEL THE AFFECT OF TROPICAL
STORM ERIKA...SEE SPECIAL FEATURES ABOVE.

ATLANTIC OCEAN...
THE MAIN FOCUS IS TROPICAL STORM ERIKA LOCATED VERY NEAR
GUADELOUPE...SEE SPECIAL FEATURES ABOVE. IN THE W ATLC...AS OF
2100 UTC...A STATIONARY FRONT ENTERS THE AREA NEAR 32N77W AND
EXTENDS SW TO NRN FLORIDA NEAR 29N81W AND INTO THE GULF OF
MEXICO. A PRE-FRONTAL SURFACE TROUGH IS AHEAD OF THE FRONT FROM
28N80W TO THE FLORIDA COAST NEAR 28N81W CONTINUING ACROSS THE
STATE INTO THE GULF. A SECOND SURFACE TROUGH IS ANALYZED OVER
THE NW BAHAMAS FROM 30N77W TO 24N78W. SURFACE CONVERGENCE NEAR
THESE BOUNDARIES IS SUPPORTING ISOLATED SHOWERS/POSSIBLE
THUNDERSTORMS FROM CUBA NWD OUT OF THE DISCUSSION AREA W OF 73W.
THE FRONT IS SUPPORTED BY AN UPPER LEVEL TROUGH OVER THE ERN
CONUS. THE AFOREMENTIONED SHOWER ACTIVITY IS ENHANCED BY UPPER
LEVEL DIFFLUENCE BETWEEN THIS UPPER TROUGH AND AN UPPER LEVEL
HIGH CENTERED NEAR 28N71W. ELSEWHERE ACROSS THE ATLC...A BROAD
SURFACE RIDGE DOMINATES ANCHORED BY A 1029 MB HIGH NEAR 36N34W.
IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE IS S OF 24N BETWEEN
40W-75W IN ASSOCIATION WITH ERIKA. AN UPPER LEVEL TROUGH IS N OF
16N BETWEEN 28W-50W. A SECOND UPPER LEVEL RIDGE IS E OF 35W WITH
AXIS ALONG 16N.

$$
WALTON





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