[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 041800
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI SEP 04 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.

...SPECIAL FEATURES...

A TROPICAL WAVE EXTENDS FROM 9N24W THROUGH A 1012 MB LOW NEAR
12N24W TO 20N21W MOVING W NEAR 18 KT. VISIBLE SATELLITE IMAGERY
INDICATES AN ELONGATED LOW-LEVEL CYCLONIC CIRCULATION FOCUSED
NEAR THE SURFACE LOW WITH CIMSS WAVETRAK MODEL GUIDANCE
INDICATING A 850-500 MB LAYER OF CYCLONIC CURVATURE BETWEEN
20W-30W. THE WAVE REMAINS WITHIN A MAXIMUM AREA OF DEEP LAYER
MOISTURE AS INDICATED BY THE TOTAL PRECIPITABLE WATER IMAGERY.
SCATTERED MODERATE CONVECTION IS FROM 7N-15N BETWEEN 23W-29W.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 35W S OF 19N WITH A 1013 MB LOW ALONG THE
WAVE NEAR 14N MOVING W NEAR 12 KT. THE WAVE COINCIDES WITH A
DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER
IMAGERY. HOWEVER...VISIBLE SATELLITE IMAGERY INDICATES SAHARAN
DUST IS LOCATED TO THE W OF THE WAVE AXIS AND ALSO TO THE NE OF
SURFACE LOW. THIS SAHARAN AIR LAYER IS INHIBITING ANY
SIGNIFICANT DEEP CONVECTION WITH ONLY A SMALL AREA OF SCATTERED
MODERATE CONVECTION FROM 15N-17N BETWEEN 34W-37W.

TROPICAL WAVE IS ALONG 53W S OF 16N MOVING W NEAR 15 KT. THE
WAVE REMAINS RELATIVELY LOW-AMPLITUDE WITH A WEAKENING 850 MB
VORTICITY SIGNATURE IN THE CIMSS WAVETRAK MODEL GUIDANCE OVER
THE PAST 6-12 HOURS. SAHARAN DUST REMAINS TO THE E OF THE WAVE
AXIS AND THUS LIMITING ANY CONVECTION.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 14N16W 13N21W 11N26W 9N34W 8N37W
8N51W. CLUSTERS OF WIDELY SCATTERED MODERATE CONVECTION AND
SCATTERED SHOWERS ARE WITHIN 120 NM S OF THE ITCZ BETWEEN
33W-52W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL TROUGH COVERS THE ERN CONUS AND EXTENDS TROUGHING
OVER THE CENTRAL AND ERN GULF OF MEXICO SWD TO THE YUCATAN
PENINSULA AND CHANNEL. EMBEDDED WITHIN THE UPPER LEVEL TROUGHING
IS AN UPPER LOW CENTERED NEAR 26N85W. THESE UPPER LEVEL FEATURES
SUPPORT A SURFACE TROUGH THAT EXTENDS ACROSS THE SRN FLORIDA
PENINSULA AND ENTERS THE GULF NEAR FORT MYERS ALONG 27N87W TO
25N92W. LOW-LEVEL CONVERGENCE S OF THE SURFACE TROUGH AND MOIST
SWLY UPPER LEVEL DIVERGENT FLOW ARE GENERATING SCATTERED SHOWERS
AND ISOLATED TSTMS OVER THE SE GULF FROM 21N-25N BETWEEN
82W-24W. ANOTHER SURFACE TROUGH IS ANALYZED ACROSS THE N/CENTRAL
GULF FROM SERN LOUISIANA INTO THE OFFSHORE GULF WATERS NEAR
28N90W. LOW-LEVEL CONVERGENCE E OF THE SURFACE TROUGH IS
GENERATING SCATTERED SHOWERS AND TSTMS N OF 27N BETWEEN 83W-90W.
THE REMAINDER OF THE GULF IS BENEATH NW TO NLY FLOW ALOFT
LIMITING ANY DEEP CONVECTION...HOWEVER A FEW PASSING ISOLATED
SHOWERS ARE POSSIBLE W OF 90W AND ACROSS THE BAY OF CAMPECHE.

CARIBBEAN SEA...
THE REMNANT 1010 MB LOW OF ERIKA IS CENTERED SOUTH OF THE MONA
PASSAGE NEAR 17N68W AND IS CONTINUING TO GENERATE SCATTERED
SHOWERS AND TSTMS FROM 12N-19N BETWEEN 61W-67W INCLUDING THE
LEEWARD ISLANDS...VIRGIN ISLANDS AND PUERTO RICO. THE UPPER
LEVEL TROUGH OVER THE ERN GULF OF MEXICO COVERS THE NW CARIBBEAN
N OF 16N W OF 70W GENERATING SCATTERED SHOWERS AND ISOLATED
TSTMS NW OF LINE FROM NW HONDURAS NEAR 16N88W TO WRN CUBA NEAR
22N82W. AN UPPER LEVEL ANTICYCLONIC CIRCULATION COVERS THE
REMAINDER OF THE CARIBBEAN WITH THE UPPER HIGH ANCHORED NEAR
14N70W DRAWING TROPICAL MOISTURE OVER THE SW CARIBBEAN AND
COUPLED WITH UPPER LEVEL DIFFLUENCE IS GENERATING SCATTERED
SHOWERS AND TSTMS S OF 15N W OF 76W...INCLUDING PORTIONS OF
PANAMA...COSTA RICA AND NICARAGUA.

ATLANTIC OCEAN...
A SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR 32N78W
EXTENDING SW TO A 1014 MB LOW OFF THE COAST OF ST. AUGUSTINE
FLORIDA CONTINUING ACROSS THE SRN FLORIDA PENINSULA AND INTO THE
GULF OF MEXICO. A BROAD UPPER RIDGE REMAINS ANCHORED OVER THE W
ATLC NEAR 34N60W THAT EXTENDS UPPER LEVEL RIDGING TO THE NW
BAHAMAS. BETWEEN THIS RIDGE AND THE UPPER LEVEL LOW AND
TROUGHING ACROSS THE ERN GULF OF MEXICO...UPPER LEVEL DIFFLUENCE
IS GENERATING CLUSTERS OF SCATTERED SHOWERS AND TSTMS FROM 23N
TO BEYOND 32N BETWEEN 76W-80W. A NARROW AND ELONGATED UPPER
LEVEL TROUGH IS OVER THE CENTRAL ATLC. MOIST SWLY UPPER LEVEL
FLOW S OF THE TROUGH AXIS AND UPPER LEVEL DIFFLUENCE IN THE
VICINITY OF THE UPPER TROUGH IS PRODUCING AN AREA OF SCATTERED
SHOWERS WITHIN 150 NM OF A LINE FROM 28N60W TO 22N52W. ELSEWHERE
ACROSS THE REMAINDER OF THE CENTRAL AND ERN ATLC...A BROAD
SURFACE RIDGE IS N OF 22N E OF 70W PROVIDES GENERALLY FAIR
WEATHER. THE SURFACE RIDGE IS ANCHORED BY A 1024 MB HIGH
CENTERED NEAR 31N51W AND ANOTHER 1027 MB HIGH CENTERED S OF THE
AZORES NEAR 37N29W.

$$
HUFFMAN


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