[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 272354
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED JUL 27 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 FEATURE...

TROPICAL STORM FRANKLIN CENTERED NEAR 33.9N 69.3W...OR ABOUT 250
NM WNW OF BERMUDA...AT 27/2100 UTC MOVING N 6 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1000 MB. MAXIMUM SUSTAINED WIND
SPEED HAS INCREASED SLIGHTLY TO 45 KT GUSTS TO 55 KT. SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/
WTNT21 KNHC FOR MORE DETAILS.  VERTICAL WIND SHEAR HAS LESSENED
A LITTLE TODAY... ALLOWED CONVECTION TO FORM CLOSER TO THE
CENTER OF FRANKLIN AND INTENSIFY.  DEEP TSTMS ARE STILL ON THE S
SIDE OF THE CIRCULATION BUT MORE SYMMETRIC THAN YESTERDAY.
SCATTERED MODERATE CONVECTION IS FROM 32.5N-34.5N BETWEEN
69W-71W.  FRANKLIN STILL HAS ABOUT 24-36 HOURS OF RELATIVELY
LIGHT SHEAR TO INTENSIFY BEFORE AN UPPER TROUGH OVER N AMERICA
BEGINS TO IMPACT STRONG SHEAR ON THE SYSTEM.

...TROPICAL WAVES...

E ATLC TROPICAL WAVE ALONG 32W/33W S OF 19N MOVING W 15 KT.
WEAK LOW/MID-LEVEL CIRCULATION NOTED NEAR 11N ON THE WAVE AXIS.
CONVECTION HAS BEEN INTERMITTENT WITH OCCASIONAL EVIDENCE OF
BANDING FEATURES TRYING TO FORM.  MODERATE ELY SHEAR IS
AFFECTING THE WAVE BUT IT REMAINS IN A MOIST ENVIRONMENT WITH
NONE OF THE DRY AIR IN THE LOW/MID LEVELS THAT OTHER WAVES HAVE
HAD TO DEAL WITH RECENTLY.  ISOLATED MODERATE CONVECTION IS
WITHIN 75 NM OF 11N34W.

CENTRAL ATLANTIC TROPICAL WAVE LOCATED 650 NM E OF THE LESSER
ANTILLES ALONG 48W/49W S OF 22N MOVING W 20 KT. A WEAK 1013 MB
LOW IS LOCATED ALONG THE AXIS NEAR 11N47W...EMBEDDED WITHIN THE
ITCZ.  THE WAVE CONTINUES TO GAIN CONVECTION COMPARED TO
YESTERDAY... THOUGH MOST OF IT IS FAR AWAY FROM ANY LOW-LEVEL
CENTER IN THE NORTHERN PART OF THE WAVE ENHANCED BY SHEAR FROM
AN UPPER TROUGH.  WIDELY SCATTERED MODERATE CONVECTION IS FROM
16N-19N BETWEEN 46W-51W WITH MORE ISOLATED ACTIVITY BETWEEN THE
SAME LONGITUDE SOUTHWARD TO 11N.  COMPUTER MODELS SUGGEST THAT
THE NORTHERN END OF THE WAVE COULD EVENTUALLY BECOME THE MORE
DOMINANT PORTION WITH THE GREATEST POTENTIAL FOR ANY TROPICAL
CYCLONE DEVELOPMENT...THOUGH VERTICAL WIND SHEAR IS MARGINAL.
AN INITIAL SURGE OF MOISTURE IS MOVING THRU THE WINDWARD ISLANDS
TONIGHT... WITH THE MOST SIGNIFICANT MOISTURE TO REACH THE
LEEWARD ISLANDS LATE THU... OVERSPREADING THE REST OF THE LESSER
ANTILLES ON FRI INTO PUERTO RICO POSSIBLY LATE FRI.  THE GFS
SUGGESTS THE HEAVIEST RAINFALL WILL STAY N OF THE ISLANDS
THOUGH.

W CARIBBEAN TROPICAL WAVE ALONG 81W S OF 16N MOVING W NEAR 20
KT.  VERY FAST LOW-LEVEL FLOW AND DRY AIR ARE MASKING ANY
TYPICAL WAVE SIGNALS.  A FEW TSTMS ARE IN THE EXTREME SW
CARIBBEAN... OTHERWISE THE WAVE POSITION IS BASED ON
EXTRAPOLATION.

TROPICAL WAVE OVER SOUTHERN MEXICO HAS LEFT THE AREA.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 12N16W 10N26W 16N46W... THEN ALONG
9N50W TO 10N60W.  THE ITCZ IS NOT PARTICULARLY WELL-DEFINED W OF
48W.  ISOLATED MODERATE CONVECTION IS WITHIN 60 NM OF
10.5N58.5W.  WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 60
NM OF A LINE FROM 7N27W 10.5N26W TO 11.5N22W. TSTMS NEAR 22W ARE
LIKELY ASSOCIATED WITH A TROPICAL WAVE THAT MAY ADDED TO THE
SURFACE MAP AT 0000 UTC.

...DISCUSSION...

GULF OF MEXICO...
A SHARP UPPER TROF/SMALL CLOSED LOW...OBSERVED IN WATER VAPOR
IMAGERY...IS JUST N OF MONTERREY SERVING AS A FOCUSING MECHANISM
FOR INLAND SHOWERS/TSTMS.   SFC RIDGE IS DEPRESSED WELL S OF
AVERAGE...EXTENDING FROM W CUBA TO A 1018 MB CENTER NEAR 24N90W
NW TO SE TEXAS WITH SOME DUST NOTED S AND W OF THE RIDGE AXIS.
WEAK 1014 MB LOW IS CENTERED NEAR NAPLES FLORIDA BUT IS
DISSIPATING.  IN THE UPPER LEVELS... GENERALLY E TO NE FLOW IS
OVER THE REGION FROM HIGH PRESSURE EXTENDING FROM SW GEORGIA
INTO CENTRAL TEXAS WITH A PERSISTENT INVERTED TROUGH EXTENDING
FROM NE YUCATAN TO SE LOUISIANA.  THE TROUGH IS RESPONSIBLE FOR
ANOTHER TYPICAL CONVECTION DAY IN SE LOUISIANA WHILE AREAS
SURROUNDING LOUISIANA ARE QUITE SUPPRESSED.  A COLD FRONT OVER
CNTRL TEXAS AND NRN MEXICO WILL APPROACH THE NW GULF COAST
TONIGHT AND WILL INCREASE THE CHANCE OF WIDELY SCATTERED
SHOWERS/TSTMS OVER THE N GULF WATERS THROUGH THE WEEKEND.

CARIBBEAN...
DRY AIR AND HAZY SKIES ARE THE RULE OVER THE CARIBBEAN TODAY
WITH VERY LITTLE SIGNIFICANT WEATHER TO SPEAK OF. ISOLATED TSTMS
HAVE FORMED OVER THE HIGHER TERRAIN OF THE GREATER ANTILLES
DURING THE DIURNAL HEATING PERIOD... BUT ARE QUICKLY
DISSIPATING.  VISIBILITIES HAVE IMPROVED OVER THE LESSER
ANTILLES NOW THAT THE MAIN SURGE OF AFRICAN DUST HAS MOVED TO
THE W...BUT SEVERAL STATIONS FROM THE N COAST OF COLOMBIA TO
HISPANIOLA...THE CAYMAN ISLANDS...AND CUBA ARE STILL REPORTING
HAZE WITH VISIBILITY OCCASIONALLY DOWN TO 4-6 MILES. A BROAD
UPPER LEVEL TROUGH IS CENTERED OVER THE NW CARIBBEAN WITH SLY
WINDS PICKING UP A LITTLE MOISTURE FROM THE TOPS OF TSTMS IN THE
SW CARIBBEAN THRU CENTRAL AMERICA. OTHERWISE...STRONG SUBSIDENCE
IS OVER THE E CARIBBEAN AND HAS MADE THE ENVIRONMENT UNFAVORABLE
FOR TSTMS.

WEST/CENTRAL ATLANTIC...
T.S. FRANKLIN IS N OF THE AREA WITH A SMALL ANTICYCLONE FORMING
NEAR 32N70W JUST S OF THE STORM.  NARROW MID/UPPER TROUGH
EXTENDING FROM THE SE BAHAMAS TO 27N74W CONTROLS THE REST OF THE
W ATLC W OF 70W BUT UPPER RIDGING FROM S OF FRANKLIN RUNS SE TO
20N55W WITH PLENTY OF HIGH CLOUDS/INCREASED UPPER MOISTURE N OF
20N BETWEEN 55W-68W.  A SURFACE TROUGH FROM PUERTO RICO TO NEAR
23N63W IS RESPONSIBLE FOR A FEW SHOWERS WITHIN 90 NM OF THE
TROUGH AXIS.  EARLIER TSTM ACTIVITY OVER THE NW BAHAMAS HAS
DISSIPATED AS THE SURFACE TROUGH IN THE AREA IS BECOMING
ILL-DEFINED.  A CHANGE IN LOW/MID LEVEL WINDS COULD BRING A
LITTLE BIT OF AFRICAN DUST INTO THE SUNSHINE STATE OVER THE
WEEKEND THOUGH THE CONCENTRATION HAS LESSENED OVER THE PAST FEW
DAYS.  THE MID-OCEANIC TROUGH LIES FROM 30N50W TO 20N54W AND IS
SHEARING THE NORTHERN END OF THE TROPICAL WAVE APPROACHING 50W.

EAST ATLANTIC...
A 1026 MB HIGH IS CENTERED NEAR 34N49W WITH THE SUBTROPICAL
RIDGE CONTINUING ESE TO THE SOUTHERN PORTION OF 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 TRPCL WAVE LOCATED NEAR 47W 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.

$$
BLAKE

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