[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 242357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN JUL 24 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM
THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON
SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...

TROPICAL STORM GERT IS CENTERED NEAR 21.8N 97.6W AT 25/0000 UTC
OR ABOUT 35 MILES SE OF TAMPICO MEXICO MOVING WNW AT 8 KT.
MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
AND THE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT2/WTNT32
KNHC FOR MORE DETAILS. A NOAA PLANE FOUND THAT GERT WAS TRYING
TO ORGANIZE RIGHT BEFORE LANDFALL WITH THE PRESSURE FALLING
SEVERAL MILLIBARS AND THE WINDS INCREASING.  THE SATELLITE
PRESENTATION IS IMPROVING WITH BANDING FEATURES AROUND A CENTER
THAT IS TRYING TO CONSOLIDATE NEAR THE MEXICAN COAST S OF
TAMPICO.  WIDELY SCATTERED MODERATE TO STRONG CONVECTION IS FROM
20N-23.5N BETWEEN 94W-99W.  HEAVY RAINS ARE EXPECTED TO BE THE
MAIN THREAT FROM GERT AS IT INTERACTS WITH THE HIGH TERRAIN.

TROPICAL STORM FRANKLIN IS CENTERED NEAR 31.4N 70.9W AT 24/2100
UTC MOVING ENE AT 8 KT. MAXIMUM SUSTAINED WIND SPEED IS 45 KT
WITH GUSTS TO 55 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1004
MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.  NW SHEAR HAS TOTALLY
EXPOSED THE CENTER OF THE CYCLONE WITH STRONG CONVECTION LYING
ABOUT 45 NM SE OF THE CENTER.  FURTHER WEAKENING IS EXPECTED AS
THE NLY SHEAR CONTINUES.  WIDELY SCATTERED MODERATE CONVECTION
FROM 28.5N-31N BETWEEN 67W-71W.

...TROPICAL WAVES...

E ATLC TROPICAL WAVE IS ALONG 26W S OF 15N MOVING W 10-15 KT.
SATELLITE IMAGERY INDICATES THAT A LOW MAY BE FORMING ALONG THE
WAVE NEAR 12N.  SCATTERED MODERATE CONVECTION IS N OF THE
POSSIBLE CIRCULATION FROM 11N-13N BETWEEN 25W-27W BUT IS
DISORGANIZED AT THE PRESENT TIME.  THE WAVE IS PART OF THE
LARGER MORE ITCZ-RELATED CIRCULATION EXTENDING TO THE SW.  A FEW
SHOWERS ARE NEAR THE CAPE VERDE ISLANDS... OTHERWISE
BROKEN/OVERCAST LOW/MID CLOUDS ARE FROM 13N-18N BETWEEN 24W-32W.

W-CENTRAL ATLC TROPICAL WAVE FROM GUYANA TO 20N52W MOVING W NEAR
20 KT.  SURFACE DATA INDICATES THE WAVE IS STRONGLY TILTED FROM
SW TO NE WITH THE MID-LEVEL PORTION OF THE WAVE LAGGING BEHIND
THE SURFACE REFLECTION.  SHOWERS/TSTMS PUSHED THRU THE WINDWARD
ISLANDS TODAY AHEAD OF THE WAVE AXIS WITH WIDELY SCATTERED TSTMS
NEAR MARGARITA ISLAND.  COMPUTER MODELS SUGGEST THAT THE WAVE
WILL FRACTURE IN THE NEXT DAY OR TWO WITH ONE PORTION MOVING
EASTWARD THRU THE LEEWARD ISLANDS AND ANOTHER PART MOVING MORE
TO THE NW IN RESPONSE TO A STRONG MID/UPPER TROUGH ALONG 55W.
SLIGHTLY HIGHER-THAN-AVERAGE CHANCES OF RAIN ARE LIKELY IN THE
WINDWARD ISLANDS WITH MOIST SE FLOW LIKELY FOR THE NEXT COUPLE
OF DAYS.

W CARIBBEAN TROPICAL WAVE FROM THE CAYMAN ISLANDS INTO PANAMA
JAMAICA ALONG 81W/82W MOVING W 25 KT.  LONG-TERM SATELLITE LOOPS
SUGGEST THAT THE WAVE ACCELERATED AS IT MOVED THRU THE CARIBBEAN
WITH TSTMS SW OF GRAND CAYMAN LIKELY MARKING THE WAVE'S
POSITION.  THIS WAVE IS ALSO THE LEADING EDGE OF AFRICAN DUST
BUT MOST OF THE DUST IS STILL IN THE CARIBBEAN SEA.  ISOLATED
MODERATE CONVECTION WITHIN 75 NM OF 17N83W.

CENTRAL AMERICA TROPICAL WAVE HAS MOVED INTO THE EPAC AND IS OUT
OF THE AREA.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 13N16W 12N23W 7N33W 12N50W 9N61W.
WIDELY SCATTERED MODERATE CONVECTION IS FROM 4N-10N BETWEEN
30W-45W.

...DISCUSSION...

GULF OF MEXICO AND FLORIDA...
MID/UPPER HIGH OVER THE W GULF DOMINATES THE LARGE SCALE PATTERN
ACROSS THE AREA. DIFFLUENT FLOW ON THE SW SIDE OF THE HIGH
CONTINUES TO PROVIDE GOOD OUTFLOW OVER TROPICAL STORM GERT.
ANTICYCLONIC FLOW COVERS THE GULF W OF 70W WHERE AN INVERTED
MID/UPPER TROUGH RUNS FROM NW CUBA TO 29N86W IN THE N-CENTRAL
GULF.  A LITTLE DIFFLUENCE FROM THE LOW ALONG WITH A WEAK
SURFACE TROUGH BISECTING THE FLORIDA PENINSULA CAUSING A FAIR
AMOUNT OF TSTMS OVER FLORIDA TODAY S OF 29N.  AT THE SURFACE...
1019 MB HIGH IS OVER THE NW GULF NEAR 28N92W WITH RATHER LIGHT
WINDS IN THE E GULF AND MUCH STRONGER WINDS NEAR THE TROPICAL
CYCLONE IN THE SW GULF.  N-NE MID/UPPER FLOW IS ADVECTING DRIER
AIR OVER THE NE GULF AND N FLORIDA PENINSULA. A WELL DEFINED
MOISTURE GRADIENT EXISTS ACROSS CENTRAL FLORIDA NEAR THE SURFACE
TROUGH AXIS...WITH SCATTERED SHOWERS/TSTMS CONCENTRATED ALONG
AND S OF THE BOUNDARY. THE SURFACE LOW AND TROUGH ARE EXPECTED
TO MOVE SLOWLY S OVER THE NEXT 24 HOURS...WITH HIGHER RAIN
CHANCES OVER THE SOUTHERN HALF OF THE FLORIDA PENINSULA.

CARIBBEAN...
WATER VAPOR IMAGERY SHOWS VERY LITTLE DEEP MOISTURE OVER MOST OF
THE CARIBBEAN WITH MOST DEEP CONVECTION ASSOCIATED WITH THE
TROPICAL WAVES. DRY AIR WITH SUSPENDED AFRICAN DUST IS SPREADING
W INTO THE WESTERN CARIBBEAN THOUGH IT APPEARS TO BE THINNING A
BIT AS IT MOVES WESTWARD. THE MAIN UPPER LEVEL FEATURE IS A
TROUGH AXIS EXTENDING FROM THE EASTERN DOMINICAN REPUBLIC TO THE
SW CARIBBEAN NEAR 12N81W. THE TROUGH DIVIDES NE FLOW OVER THE W
CARIBBEAN FROM SW FLOW OVER THE CENTRAL/E CARIBBEAN AS A NARROW
MID/UPPER RIDGE AXIS SNEAKS INTO THE S CARIBBEAN FROM BARBADOS
TO 11N78W THRU N COLOMBIA AND THE ABC ISLANDS.  INCREASING RAIN
CHANCES ARE LIKELY OVERNIGHT INTO TOMORROW FOR N VENEZUELA AND
THE ADJACENT ISLANDS INCLUDING THE ABC CHAIN AS THE SURGE OF
MOISTURE MOVES THRU THE AREA.

ATLANTIC...
MID/UPPER LEVEL TROUGH MOVING SE EXTENDS FROM 32N68W TO THE NE
FLORIDA COAST NEAR 29N81W. NORTHERLY FLOW N OF THE TROUGH IS
PRODUCING A RATHER HOSTILE ENVIRONMENT OVER TROPICAL STORM
FRANKLIN WITH PLENTY OF SHEAR. THE REST OF WESTERN ATLANTIC IS
DOMINATED BY DEEP LAYERED HIGH PRESSURE NEAR 25N65W AND
SUBSIDENCE ALOFT.  NARROW MID-OCEANIC TROUGH LIES ALONG
31N51W-18N57W...WITH SMALL CYCLONIC CIRCULATION NEAR THE
DOMINICAN REPUBLIC NEAR 19N69W SPLIT OFF FROM THE TROUGH. WEAK
LOW LEVEL CONVERGENCE IS N OF RIDGE AXIS FROM 31N36W-25N67W AND
IS INTERACTING WITH THE UPPER TROUGH TO PRODUCE ISOLATED
MODERATE CONVECTION WITHIN 60 NM OF LINE 32N51W-24N60W. THE
EASTERN ATLANTIC IS DOMINATED BY RIDGE ALOFT ALONG 16N E OF
30W...WITH MAIN HIGH CENTER NEAR 14N54W RIDGING SW TO NEAR
BARBADOS.  VERY DRY AIR IS PRESENT W OF 45W IN THE DEEP TROPICS
ASSOCIATED WITH THE SAHARAN DUST OUTBREAK.  DEEP EASTERLY FLOW S
OF THE RIDGE HAS ENOUGH UPPER DIFFLUENCE AND AVAILABLE MOISTURE
TO SUPPORT CONVECTION NEAR THE ITCZ AND E ATLC TROPICAL WAVE.
LARGE AREA OF SAHARAN DUST COVERS MOST OF EASTERN ATLANTIC...
WITH MAIN CONCENTRATIONS S OF 23N W OF 42W AND N OF 17N E OF 40W
TO THE AFRICAN COAST.

$$
BLAKE


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