[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 281102
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT THU JUL 28 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 0600 UTC SURFACE ANALYSIS AND
SATELLITE IMAGERY THROUGH 1045 UTC.

...SPECIAL FEATURE...

TROPICAL STORM FRANKLIN CENTER NEAR 35.5N 69.2W...OR ABOUT
335 MILES/540 KM NORTHWEST OF BERMUDA...AT 28/0900 UTC MOVING
NORTH 8 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1000 MB.
THE MAXIMUM SUSTAINED WIND SPEED IS 45 KT GUSTS 55 KT. SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/
WTNT21 KNHC FOR MORE DETAILS. THE LOW LEVEL CIRCULATION IS
MOSTLY OBSCURED BY THE CONVECTIVE ACTIVITY AND CIRRUS OUTFLOW.
THE SHOWERS AND THUNDERSTORMS WHICH HAD DEVELOPED FROM 33N TO
35N BETWEEN 68W AND 70W HAS WEAKENED AS THE CLOUD TOP
TEMPERATURES HAVE WARMED. THE NEWEST BURST OF SHOWERS AND
THUNDERSTORMS IS OCCURRING FROM 35N TO 36N BETWEEN 69W AND 70W.
A SHORT WINDOW OF OPPORTUNITY OF ABOUT 24 HOURS EXISTS FOR
FRANKLIN TO STRENGTHEN SLIGHTLY. WEAKENING WITHIN AN ENVIRONMENT
OF INCREASING WESTERLY VERTICAL WIND SHEAR IS ANTICIPATED
THEREAFTER UNTIL FRANKLIN BECOMES EXTRATROPICAL AND MERGES WITH
A FRONTAL SYSTEM IN ABOUT 3 TO 4 DAYS.

...TROPICAL WAVES...

EASTERN ATLANTIC OCEAN TROPICAL WAVE IS ALONG 23W/24W SOUTH OF
15N MOVING WEST 15 KT. WIDELY SCATTERED TO SCATTERED MODERATE/
ISOLATED STRONG SHOWERS AND THUNDERSTORMS FROM 5N TO 8N BETWEEN
20W AND 24W...AND MORE ISOLATED IN NATURE FROM 4N TO 12N BETWEEN
27W AND 30W.

EASTERN ATLANTIC OCEAN TROPICAL WAVE ALONG 35W/36W SOUTH OF 18N
MOVING WEST 15 KT. A POSSIBLE LOW TO MIDDLE LEVEL CYCLONIC
CIRCULATION IS NEAR 11N ALONG 36W ALONG THE WAVE. ISOLATED TO
WIDELY SCATTERED MODERATE/LOCALLY STRONG SHOWERS AND
THUNDERSTORMS FROM 7N TO 13N BETWEEN 34W AND 40W.

CENTRAL ATLANTIC TROPICAL WAVE ALONG 22N52W 17N54W TO A 1013 MB
LOW PRESSURE CENTER NEAR 15N54W TO 10N54W...MOVING WEST 20 KT.
NUMEROUS STRONG SHOWERS AND THUNDERSTORMS FROM 17N TO 20N
BETWEEN 47W AND 50W...AND FROM 17N TO 21N BETWEEN 50W AND 54W.
SCATTERED MODERATE TO ISOLATED STRONG SHOWERS AND THUNDERSTORMS
ELSEWHERE FROM 14N TO 16N BETWEEN 56W AND 58W. THIS WAVE SHOWS
UP QUITE WELL IN SATELLITE IMAGERY. IT MAY REACH THE EASTERN
CARIBBEAN SEA ISLANDS DURING THE NEXT 24 TO 36 HOURS...OR AT
LEAST POSSIBLY SOME OF THE SHOWERS TRAVELING WITH IT MAY REACH
THE ISLANDS BEFORE THE ACTUAL WAVE ARRIVES. COMPUTER MODELS
SUGGEST THAT THE NORTHERN END OF THE WAVE EVENTUALLY MAY BECOME
THE MORE DOMINANT PART WITH THE GREATEST POTENTIAL FOR ANY
TROPICAL CYCLONE DEVELOPMENT...THOUGH VERTICAL WIND SHEAR IS
MARGINAL. THE MOST SIGNIFICANT MOISTURE IS SET TO REACH THE
LEEWARD ISLANDS LATE THURSDAY...OVERSPREADING THE REST OF THE
LESSER ANTILLES ON FRIDAY INTO PUERTO RICO POSSIBLY LATE FRIDAY.
THE GFS MODEL THOUGH SUGGESTS THAT THE HEAVIEST RAINFALL WILL
STAY NORTH OF THE ISLANDS.

WESTERN CARIBBEAN SEA TROPICAL WAVE ALONG 84W/85W SOUTH OF 17N
MOVING WEST ABOUT 20 KT. VERY FAST LOW-LEVEL FLOW AND DRY AIR
ARE MASKING ANY TYPICAL WAVE SIGNALS. NUMEROUS STRONG ITCZ
SHOWERS AND THUNDERSTORMS IN THE SOUTHWESTERN CORNER OF THE
CARIBBEAN SEA OVER LAND AND COASTAL WATERS FROM COLOMBIA TO
SOUTHEASTERN NICARAGUA FROM 5N TO 10N BETWEEN 75W AND 86W.

...THE ITCZ...

ITCZ 14N15W 11N21W...10N25W 10N32W...11N37W 12N44W 15N48W...
10N55W 10N62W. ISOLATED MODERATE SHOWERS...SOME WEAKENING AND
SOME DEVELOPING RECENTLY...FROM 5N TO 7N BETWEEN 11W AND 13W...
FROM 5N TO 6N BETWEEN 15W AND 16W...AND FROM 3N TO 10N BETWEEN
46W AND 53W.

...DISCUSSION...

THE GULF OF MEXICO...
ISOLATED MODERATE SHOWERS STRETCH FROM THE SOUTHEASTERN GULF
TO THE CENTRAL AND WEST CENTRAL GULF. ISOLATED MODERATE TO
LOCALLY STRONG SHOWERS AND THUNDERSTORMS HAVE FORMED ALONG THE
COAST OF LOUISIANA FROM THE MISSISSIPPI BORDER TO THE SOUTH
CENTRAL COAST...AND ALONG THE FLORIDA WEST COAST FROM 26N TO
28N. MIDDLE TO UPPER LEVEL CYCLONIC CIRCULATION CENTER IS IN
INTERIOR NORTHEASTERN MEXICO NEAR 24N100W. BROAD EAST TO
NORTHEAST FLOW ACROSS THE EASTERN GULF WATERS BECOMES CYCLONIC
WITH A MIDDLE TO UPPER LEVEL INVERTED TROUGH WHICH RUNS FROM THE
NORTHWESTERN GULF WATERS TOWARD THE SOUTHWESTERN CORNER OF THE
AREA/YUCATAN PENINSULA. MIDDLE TO UPPER LEVEL DRY AIR IS IN
PLACE PRETTY MUCH EVERYWHERE. 1018 MB SURFACE HIGH PRESSURE
CENTER IS NEAR 27N88W...WITH BROAD ANTICYCLONIC FLOW. A SURFACE
COLD FRONT OVER CENTRAL TEXAS AND NORTHERN MEXICO WILL APPROACH
THE NORTHWESTERN GULF COAST THROUGHOUT THE REST OF TODAY AND
WILL INCREASE THE CHANCE OF WIDELY SCATTERED SHOWERS AND
THUNDERSTORMS IN THE NORTHERN GULF WATERS THROUGH THE WEEKEND.

THE CARIBBEAN SEA...
MIDDLE TO UPPER LEVEL DRY AIR COVERS MOST OF THE AREA...EXCEPT
FOR THE EXTREME NORTHEASTERN CORNER AND THE EXTREME SOUTHEASTERN
CORNER. MIDDLE TO UPPER LEVEL NORTHEASTERLY WIND FLOW IS PUSHING
SOME UPPER LEVEL MOISTURE INTO THE EXTREME NORTHEASTERN CORNER
AND UPPER LEVEL MOISTURE WITH SOME BITS OF ITCZ CONVECTIVE
ACTIVITY ARE TRYING TO PUSH THEIR WAY INTO THE EXTREME
SOUTHEASTERN CORNER. BROAD UPPER LEVEL ANTICYCLONIC FLOW COVERS
THE AREA FROM 10N TO 20N BETWEEN 70W AND 80W. MIDDLE TO UPPER
LEVEL CYCLONIC FLOW STRETCHES INTO THE NORTHWESTERN CORNER OF
THE AREA FROM THE INVERTED GULF OF MEXICO TROUGH.

THE WESTERN AND CENTRAL ATLANTIC OCEAN...
T.S. FRANKLIN IS JUST NORTH OF THE AREA. CYCLONIC FLOW IS
CENTERED NEAR 26N58W...ABOUT 760 NM EAST-SOUTHEAST OF FRANKLIN.
ANOTHER CYCLONIC CIRCULATION CENTER IS NEAR 26N75W...ABOUT 580
NM SOUTH-SOUTHWEST OF FRANKLIN. A SURFACE TROUGH RUNS FROM
28N75W TO THE BAHAMAS NEAR 25N76W TO 23N77W. ISOLATED MODERATE
SHOWERS FROM 23N TO 26N BETWEEN 73W AND 77W. UPPER LEVEL
ANTICYCLONIC FLOW WITH A SHORTWAVE RIDGE IS JUST EAST OF THIS
26N75W CYCLONIC CENTER. A SURFACE TROUGH CONTINUES ALONG 68W
FROM THE MONA PASSAGE TO 25N. ISOLATED MODERATE SHOWERS FROM
20N TO 30N BETWEEN 55W AND 70W. THE MID-OCEANIC TROUGH LIES
FROM 30N50W TO 20N54W AND IS SHEARING THE NORTHERN END OF THE
TROPICAL WAVE APPROACHING 50W.

THE EASTERN ATLANTIC OCEAN...
A 1026 MB HIGH PRESSURE CENTER IS NEAR 31N49W...WITH THE
SUBTROPICAL RIDGE CONTINUING EAST-SOUTHEAST TO THE SOUTHERN
SECTION OF THE WESTERN SAHARA. AN UPPER HIGH IS CENTERED FARTHER
S NEAR 16N40W WITH RIDGE EXTENDING NW TO 30N44W...AND THIS IS
KEEPING THE DEEPEST ELY FLOW S OF ABOUT 16N. THE 22N52W TO 10N52W
TROPICAL WAVE IS A RATHER DEEP FEATURE...HIGHLIGHTED BY THE
INVERTED TROF NOTED IN THE UPPER LEVELS ALONG 52W. IN THE NE
ATLC...MID-LATITUDE TROUGH HAS DIPPED INTO THE AREA LONG 34N16W
TO 26N21W WITH THE ASSOCIATED COLD FRONT NOW DISSIPATED IN THE
AREA.  THE MOST NOTICEABLE EFFECT IS THE SIGNIFICANT WIND
DIRECTION CHANGE IN THE NE ATLC FROM STRONG NE TO WEAK NW NEAR
THE CANARY ISLANDS BECAUSE OF THE COMPLETE ABSENCE OF THE
SUBTROPICAL RIDGE TYPICALLY NEAR THE AZORES. WATER VAPOR
SUGGESTS THE TROPICAL ATLC IS MUCH MORE MOIST ALOFT THAN EARLIER
WITH LESS SUBSIDENCE NOTED ESPECIALLY E OF 50W. TRADE WINDS
REMAIN WEAK IN THE E ATLC WITH THE ONLY ENHANCEMENT OF TRADES
NEAR THE NORTHERN PART OF THE TROPICAL WAVE APPROACHING 50W.

$$
MT



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