[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 120551
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT TUE 12 OCT 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA... GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND ATLC 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0345 UTC.

...TROPICAL WAVES...
E ATLC TROPICAL WAVE ALONG MEAN AXIS OF 36W S OF 17N MOVING W 10
KT. WAVE REMAINS VERY WEAK WITH A FAINT V-SHAPE SIGNATURE IN
SATELLITE IMAGERY AS ITS PRIMARY IDENTIFYING FEATURE. NO DEEP
CONVECTION IS EVIDENT ALONG THE WAVE...WITH WIDELY SCATTERED
ITCZ-RELATED CONVECTION E OF THE WAVE ALONG 8N.

TROPICAL WAVE IN THE LESSER ANTILLES NEAR 63W S OF 20N MOVING
W 10-15 KT. THE WAVE HAS LITTLE SIGNATURE IN SATELLITE PICTURES
AND IN LATEST UPPER-AIR DATA FROM THE LESSER ANTILLES AND
EASTERN CARIBBEAN SEA.

...ITCZ...
ITCZ AXIS ALONG 9N13W 7N25W 9N39W 8N48W 10N61W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION WITHIN 180 NM N OF THE AXIS
E OF 18W TO THE AFRICA COAST...AND WITHIN 90 NM EITHER SIDE OF
AXIS BETWEEN 18W-21W. WIDELY SCATTERED MODERATE CONVECTION
WITHIN 180 NM S OF AXIS BETWEEN 23W-35W...AND WITHIN 120 NM
EITHER SIDE OF AXIS BETWEEN 40W-60W.

...DISCUSSION...
GULF OF MEXICO AND ATLC W OF 70W...
THE DEEP-LAYERED LOW PRESSURE SYSTEM ASSOCIATED WITH FORMER
TROPICAL STORM MATTHEW OVER THE SOUTH-CENTRAL PLAINS STATES IS
SLOWLY MOVING N AND FURTHER AWAY FROM DISCUSSION AREA. THE AREA
IS NOW DOMINATED BY A SPRAWLING MID/UPPER LEVEL HIGH CENTERED
OVER THE YUCATAN PENINSULA. ANTICYCLONIC FLOW IS OBSERVED ON
WATER VAPOR IMAGERY AND SUPPORTED BY 0000 UTC UPPER-AIR DATA.
AN ANTICYCLONICALLY CURVED 70-80 KT JET MAX AT 200 MB EXTENDS
FROM NORTHERN MEXICO ACROSS MUCH OF TEXAS TO ACROSS THE GULF
COASTAL STATES AND N FLORIDA. THE HIGH IS HELPING TO PRODUCE
LARGE-SCALE SUBSIDENCE AND ASSOCIATED MID/UPPER LEVEL DRY AIR
OVER THE GULF AND SOUTHEASTERN UNITED STATES. AT THE SURFACE...A
WEAKENING OCCLUDED FRONT FROM THE REMNANT OF MATTHEW ACROSS THE
WESTERN FLORIDA PANHANDLE AND CONNECTS TO A WEAK 1010 MB SURFACE
LOW OVER THE EASTERN GULF NEAR 27N85W. A COLD FRONT EXTENDS S
FROM THE LOW TO JUST N OF THE YUCATAN CHANNEL WHERE IT BECOMES
STATIONARY TO JUST OFF THE N COAST OF THE YUCATAN PENINSULA AND
SOUTHERN BAY OF CAMPECHE. THE FRONTAL SYSTEM AND LOW SEPARATE
THE DRY AIR TO THE W FROM DEEP-LAYERED MOISTURE OVER MUCH OF
FLORIDA...THE NW BAHAMAS...AND THE YUCATAN PENINSULA. RADAR DATA
FROM SOUTH FLORIDA INDICATES NUMEROUS SHOWERS AND TSTMS
APPROACHING THE SW FLORIDA COAST...WITH STRATIFORM PRECIPITATION
OVER THE REST OF S FLORIDA. THE FRONT IS LIKELY INTERACTING WITH
DIURNAL SEA BREEZES TO PRODUCE SCATTERED STRONG CONVECTION OVER
THE YUCATAN PENINSULA AND SOUTHERN BAY OF CAMPECHE...ALTHOUGH
THIS ACTIVITY HAS DIMINISHED IN THE PAST FEW HOURS. THE LOW AND
FRONTAL SYSTEM WILL MOVE SLOWLY E THROUGH THE DAY...BRINGING
WITH IT A WET DAY ACROSS SOUTH FLORIDA. DRIER AIR WILL GRADUALLY
WORK ITS WAY ACROSS THE REST OF FLORIDA AS THE MID/UPPER LEVEL
HIGH SHIFTS EASTWARD IN RESPONSE TO A TROUGH MOVING E OVER THE
MISSISSIPPI VALLEY.

CARIBBEAN SEA...
MID/UPPER LEVEL HIGH OVER THE YUCATAN PENINSULA EXTENDS EASTWARD
ACROSS MUCH OF CARIBBEAN SEA. A CYCLONIC SHEAR AXIS ENTERS AREA
NEAR THE VIRGIN ISLANDS AND EXTENDS SW TO 14N70W-11N80W. NW OF
THE SHEAR AXIS...ANTICYCLONIC FLOW AND DRIER MID/UPPER LEVEL AIR
PREVAILS...EXCEPT FOR THE FAR WESTERN CARIBBEAN WHERE SCATTERED
SHOWERS AND TSTMS ARE FORMING NEAR 86W E OF A WEAK 1010 MB LOW
OVER BELIZE. SCATTERED TSTMS ARE ALSO MOVING SW OVER HONDURAS
AND EL SALVADOR. A BAND OF MID AND HIGH LEVEL MOISTURE IS ALONG
AND JUST S OF SHEAR AXIS FROM THE ITCZ AXIS ALONG 11N IN THE SW
CARIBBEAN TO THE LEEWARD ISLANDS. THE SHEAR AXIS IS EXPECTED TO
MOVE SE AND WEAKEN OVER THE NEXT 24 HOURS...LEAVING THE HIGH AS
THE MAIN FEATURE ACROSS THE AREA. SHOWERS/TSTMS WILL BE
CONCENTRATED OVER PARTS OF CENTRAL AMERICA AND YUCATAN PENINSULA
AS WELL AS THE SOUTHERN CARIBBEAN AND LEEWARD ISLANDS NEAR THE
SHEAR AXIS.

SUBTROPICAL ATLC E OF 70W...
HIGH AMPLITUDE MID/UPPER LEVEL FEATURES ARE AFFECTING THIS AREA.
SOUTHERN EDGE OF DEEP-LAYERED LOW ASSOCIATED WITH THE
EXTRATROPICAL REMNANT OF SUBTROPICAL STORM NICOLE ARE SKIRTING
THE NORTHERN PORTION OF THE AREA W OF 60W...INDICATED BY A 80-90
KT JET MAX AT 200 MB FROM N FLORIDA ACROSS BERMUDA. SURFACE COLD
FRONT ENTERS AREA NEAR 32N62W AND EXTENDS SW TO 28N73W...THEN
TURNS NW AND BECOMES STATIONARY TO NEAR THE FLORIDA/GEORGIA
BORDER. BROKEN/LOCALLY OVERCAST LOW/MID CLOUDS ARE ALONG THE
FRONT...WITH AREAS OF BROKEN HIGH CLOUDS STREAMING E ALONG AND S
OF THE JET MAX. COLD AIR ADVECTION STRATOCUMULUS CLOUDS ARE NW
OF THE FRONT AND AFFECTING BERMUDA.  FURTHER E...MID/UPPER LEVEL
CYCLONIC CIRCULATION NEAR 29N57W IS MOVING NE AND HAS A TROUGH
WHICH EXTENDS SW TO THE VIRGIN ISLANDS WHERE IT CONNECTS TO THE
SHEAR AXIS OVER THE CARIBBEAN SEA. THIS FEATURE IS ENHANCING
ISOLATED SHOWERS N OF PUERTO RICO AND THE NORTHERN LEEWARD
ISLANDS...WITH SCATTERED MODERATE CONVECTION E OF THE CYCLONIC
CIRCULATION FROM 26N-32N BETWEEN 50W-55W. MID/UPPER RIDGE AXIS
IS ALONG 48W AND IS MOVING E. PLENTY OF HIGH CLOUDS ARE PRESENT
OVER THE RIDGE AXIS DUE TO CIRRUS BLOWOFF FROM UPSTREAM TSTMS.
A LARGE AND POWERFUL DEEP-LAYERED LOW IS NEAR 32N32W MOVING SSW
INTO THE AREA.  THE LOW NEEDS TO BE WATCHED FOR A TRANSITION
INTO A SUBTROPICAL OR TROPICAL CYCLONE WITH IT MOVING OVER
PROGRESSIVELY WARM...AND WARMER-THAN-AVERAGE...SEA SURFACE
TEMPERATURES AND SCATTERED MODERATE CONVECTION CONTINUING TO
FORM WITHIN 120-150 NM FROM THE CENTER. ASSOCIATED COLD FRONT
ENTERS THE E ATLC NEAR 32N24W SW TO 23N33W...THEN ENE TO 25N46W.
LARGE AREA OF MULTI-LAYERED BROKEN/OVERCAST CLOUDS AND WIDELY
SCATTERED SHOWERS/TSTMS ARE N OF 23N BETWEEN 21W-29W WITH
SCATTERED STRONG CONVECTION DEVELOPING NEAR TAIL END OF FRONT
NEAR 25N49W. THE MID/UPPER FLOW IS EXPECTED TO REMAIN HIGHLY
AMPLIFIED ACROSS THE SUBTROPICAL ATLC OVER THE NEXT 24-36 HOURS
AS THE LARGE E ATLC LOW MOVES SLOWLY SSW AND A BLOCKING HIGH
DEVELOPS OVER THE N CENTRAL ATLC BETWEEN 40W-50W.

TROPICAL ATLC...
MID/UPPER LEVEL HIGH NEAR 16N53W IS PRODUCING ANTICYCLONIC FLOW
OVER TROPICAL ATLC W OF 40W. A WEAK MID-LEVEL TROUGH FROM 20N55W
TO 17N56W IS PRODUCING WIDELY SCATTERED MODERATE CONVECTION FROM
16N-19N BETWEEN 52W-55W.  OTHERWISE DEEP CONVECTION IS LIMITED
TO THE ITCZ WITH THE HIGH KEEPING A LID ON CONVECTION AS DRY
MID/UPPER AIR DOMINATES.  E OF 40W...MID/UPPER FLOW BECOMES
CYCLONIC NEAR THE BASE OF THE LARGE E ATLC LOW NEAR 32N32W. A
WEAK TROUGH AXIS FROM 20N30W TO 5N40W IS PROVIDING UPPER LEVEL
SUPPORT FOR ITCZ TSTMS E OF 40W TO NEAR THE AFRICAN COAST.

$$
MOLLEDA


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