[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 300003
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON SEP 29 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...

SUBTROPICAL STORM LAURA IS CENTERED NEAR 38.3N 48.4W AT
29/2100 UTC OR ABOUT 545 NM SSE OF CAPE RACE NEWFOUNDLAND MOVING
NNW AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 995 MB.
MAXIMUM SUSTAINED WIND SPEED IS 50 KT WITH GUSTS TO 60 KT. LAURA
IS EXPECTED TO TURN TOWARD THE N THEN NNE WITH AN INCREASE IN
FORWARD SPEED DURING THE NEXT COUPLE OF DAYS. TROPICAL STORM
FORCE WINDS EXTEND OUTWARD UP TO 210 NM FROM THE CENTER.
SCATTERED MODERATE CONVECTION IS FOUND WITHIN 150 NM OF THE
CENTER IN THE ERN SEMICIRCLE OF LAURA. LAURA IS EXPECTED TO
STRENGTHEN SOME DURING THE NEXT 24 HOURS BEFORE MOVING OVER
COLDER WATERS...AND IS EXPECTED TO TRANSITION TO A TROPICAL
STORM TONIGHT. SEE THE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCPAT2/ WTNT32 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 28W S OF 15N MOVING W 10-15 KT.
SATELLITE IMAGERY DEPICTS WELL-DEFINED INVERTED-V STRUCTURE TO
LOW/MID-LEVEL CLOUD PATTERN ALONG WAVE AXIS...WHERE COMPUTER
MODEL GUIDANCE CONFIRMS WEAK LOW LEVEL CIRCULATION. MIMIC TOTAL
PRECIPITABLE WATER PRODUCT FROM CIMSS ALSO SHOWS WAVE IS
EMBEDDED WITHIN DEEP LAYER MOISTURE MAXIMUM. ISOLATED MODERATE
CONVECTION IS WITHIN 90 NM OF WAVE AXIS S OF 6N...AND ADDITIONAL
ISOLATED MODERATE CONVECTION IS WITHIN 120 NM OF WAVE AXIS N OF
12N.

A TROPICAL WAVE IS ALONG 42W/43W FROM 10N-20N MOVING W 5-10 KT.
SATELLITE IMAGERY CONTINUES TO DEPICT BROAD-LOW LEVEL
CIRCULATION CENTERED ALONG WAVE AXIS NEAR 15N. DEEP LAYER
MOISTURE IS ALSO BROADLY DISTRIBUTED AROUND WAVE. THIS WAVE IS
DIRECTLY BENEATH AN UPPER HIGH...RESULTING IN STABLE ATMOSPHERIC
CONDITIONS PREVENTING ANY DEEP CONVECTION NEAR THE WAVE.

A TROPICAL WAVE IS ALONG 56W/57W S OF 16N MOVING W NEAR 10 KT.
OTHER THAN A WEAK ENHANCEMENT IN TOTAL PRECIPITABLE WATER NEAR
THE WAVE...THIS WAVE IS ILL-DEFINED. STABLE CONDITIONS BENEATH
AN UPPER RIDGE ARE PREVENTING DEEP CONVECTIVE DEVELOPMENT NEAR
THE WAVE.

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 12N15W 11N25W 7N33W 7N46W
10N60W. IN ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL
WAVES...CLUSTERS OF MODERATE/ISOLATED STRONG CONVECTION ARE
MOVING WESTWARD TOWARD THE W COAST OF AFRICA...AFFECTING
S SENEGAL...GAMBIA...AND GUINEA-BISSAU. ISOLATED MODERATE
CONVECTION IS FROM 3N-8N BETWEEN 36W-41W. ISOLATED MODERATE
CONVECTION IS FROM 9N-12N BETWEEN 60W-70W AFFECTING N VENEZUELA.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER TROUGH IS OVER THE W GULF...WITH THE TROUGH AXIS
EXTENDING FROM SW LOUISIANA TO THE BAY OF CAMPECHE. MOIST
SOUTHWESTERLY FLOW ALOFT IS E OF THE TROUGH AXIS...PROVIDING
UPPER LEVEL SUPPORT FOR NUMEROUS SHOWERS AND THUNDERSTORMS OVER
THE E GULF. ADDITIONALLY...A 1012 MB SURFACE LOW IS OVER THE
S/CENTRAL GULF NEAR 23N88W. A SURFACE TROUGH EXTENDS FROM THE
COAST OF FLORIDA NEAR 26N82W WESTWARD TO THE LOW AND THEN TO THE
SW OVER THE YUCATAN PENINSULA. LOW LEVEL CONVERGENCE NEAR THESE
FEATURES IS FURTHER ENHANCING THE SHOWERS AND THUNDERSTORMS OVER
THE E GULF S OF 28N...AFFECTING MUCH OF S FLORIDA AND W CUBA. TO
THE W OF THE UPPER TROUGH AXIS...DEEP LAYER DRY AIR AND
SUBSIDENCE ARE RESULTING IN FAIR WEATHER OVER THE W GULF...WHERE
A WEAK SURFACE RIDGE IS BUILDING FROM THE NW.

CARIBBEAN SEA...
AN UPPER LOW IS OVER N VENEZUELA...WITH AN UPPER HIGH LOCATED
OVER THE SW ATLANTIC. E FLOW ALOFT BETWEEN THESE FEATURES IS
SPREADING DEEP LAYER DRY AIR ACROSS MUCH OF THE CENTRAL AND
E CARIBBEAN RESULTING IN MOSTLY FAIR WEATHER...WITH ONLY
ISOLATED SHOWERS E OF 70W AND S OF 15N. A WEAK UPPER TROUGH
EXTENDS FROM CENTRAL AMERICA NORTHWARD INTO THE SW CARIBBEAN.
THIS TROUGH IS GENERATING DIFFLUENT UPPER FLOW IN THE W
CARIBBEAN...WHERE SCATTERED MODERATE CONVECTION IS OCCURRING W
OF 80W INCLUDING HONDURAS AND NICARAGUA...AS WELL AS OVER
PANAMA. CLUSTERS OF MODERATE CONVECTION OVER FAR NW VENEZUELA
ARE MOVING INTO THE ADJACENT COASTAL WATERS OF THE S CARIBBEAN.
TRADE WINDS OF 10 TO 20 KT PERSIST THROUGHOUT THE CARIBBEAN.

ATLANTIC OCEAN...
SUBTROPICAL STORM LAURA IS LOCATED IN THE N/CENTRAL ATLANTIC...
SEE SPECIAL FEATURES SECTION ABOVE. THE W ATLC IS BETWEEN AN
UPPER TROUGH OVER THE W GULF...AND AN UPPER HIGH E OF THE
BAHAMAS CENTERED NEAR 24N69W. AS A RESULT...MOIST SW FLOW ALOFT
CONTINUES OVER THE W ATLC W OF 74W....WITH SCATTERED SHOWERS AND
THUNDERSTORMS OVER THE SW ATLANTIC...AFFECTING S FLORIDA...THE
BAHAMAS...AND CUBA. THIS ACTIVITY IS BEING ENHANCED BY A SURFACE
TROUGH EXTENDING FROM S FLORIDA NEAR 27N80W EASTWARD TO NEAR
29N77W. BENEATH THE UPPER HIGH IS A 1016 MB SURFACE HIGH
CENTERED NEAR 26N67W. DRY AIR AND SUBSIDENCE ASSOCIATED WITH
THESE FEATURES COVER A LARGE AREA OF THE CENTRAL ATLC WHERE
MOSTLY FAIR WEATHER PREDOMINATES. TO THE E...AN UPPER TROUGH
COVERS PORTIONS OF THE CENTRAL ATLANTIC E OF SUBTROPICAL STORM
LAURA...AND EXTENDS FROM 32N41W SOUTHWARD TO 23N50W TO NEAR THE
LESSER ANTILLES NEAR 14N61W. STRONG FLOW ALOFT E OF THE TROUGH
AXIS IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 26N-32N
BETWEEN 36W-42W. S OF 23N...THIS UPPER TROUGH IS SHARPENED
BETWEEN THE UPPER HIGH E OF THE BAHAMAS...AND AN UPPER RIDGE
FURTHER TO THE E. THIS RIDGE COVERS MUCH OF THE E ATLC...AND
EXTENDS TO THE W OF AN UPPER HIGH NEAR 19N23W TO NEAR 17N46W. S
OF THIS RIDGE...DEEP LAYER E FLOW IS PRESENT...WITH A SURFACE
RIDGE OVER THE E ATLANTIC ALONG 31W N OF 21N.

$$
COHEN

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