[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 311733 RRA
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE JUL 31 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

TROPICAL DEPRESSION THREE HAS BEEN UPGRADED TO THE THIRD NAMED
STORM IN THE 2007 ATLANTIC SEASON...CHANTAL. TROPICAL STORM
CHANTAL WAS CENTERED NEAR 40.2N 62.7W AT 31/1500 UTC OR ABOUT
260 NM SOUTH OF HALIFAX NOVA SCOTIA AND ABOUT 575 NM SOUTHWEST
OF CAPE RACE NEWFOUNDLAND MOVING RAPIDLY NNE AT 25 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1001 MB. MAXIMUM SUSTAINED WIND
SPEED IS 45 KT WITH GUSTS TO 55 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
FOR ADDITIONAL DETAILS. SATELLITE IMAGERY SHOWS AN IMPRESSIVE
TIGHTLY WOUND CURVED BAND STRUCTURE WHICH LIES TO THE N OF THE
PARTIALLY EXPOSED LOW-LEVEL CENTER. CONVECTIVE IS MOST ORGANIZED
IN THIS BAND WHICH IS ROUGHLY WITHIN 120-150 NM NNE OF THE
CENTER. CHANTAL IS ANTICIPATED TO BEGIN IT'S EXTRATROPICAL
TRANSITION IN THE NEXT 24 HOURS OR SO AS IT CONTINUES ITS RAPID
NELY MOVEMENT TOWARD COLDER WATERS STEERED BY STRONG SWLY FLOW
AHEAD OF A DEEP LAYER TROUGH.

A 1010 MB LOW NEAR 12N51W...POSSIBLY SPAWNED BY THE RE-LOCATED
TROPICAL WAVE ALONG 59W...IS CENTERED ABOUT 520 NM E OF THE SRN
WINDWARD ISLANDS. SATELLITE IMAGERY SHOWS SOME OVERALL WEAKENING
OF THIS SYSTEM OVER THE PAST FEW HOURS WITH CLOUD TOPS WARMING
NEAR THE CENTER AND THE OVERALL CIRCULATION APPEARING RAGGED.
HOWEVER...THE WINDOW FOR FURTHER DEVELOPMENT STILL EXISTS OVER
THE NEXT COUPLE OF DAYS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 35W S OF 21N MOVING W 10-15 KT. ACCORDING
TO A LONG TERM SATELLITE LOOP AND THE CIMSS TPW PRODUCT...IT
APPEARS AS THIS WAVE LEFT BEHIND A WEAK LOW-LEVEL CIRCULATION/
SWIRL ANALYZED 1010 MB NEAR 13N28W. THE WAVE ITSELF IS STILL
NOTED WITH BROAD CURVATURE EVIDENT IN THE STRATOCUMULUS CLOUDS.
CONVECTION IS LINEAR AND CONFINED TO THE ITCZ.

TROPICAL WAVE...EARLIER DETACHED FROM THE SPECIAL FEATURE...IS
ANALYZED ACROSS THE ERN CARIB ISLANDS ALONG 59W/60W MOVING W 15
KT. SATELLITE IMAGERY SHOWS A WEAK INVERTED-V SHAPE TO THE LOW
CLOUD FIELD WITH EMBEDDED SCATTERED SHOWERS OVER THE LESSER
ANTILLES. MORE SIGNIFICANT ACTIVITY IS LOCATED NEAR THE BASE OF
WAVE DUE TO THE INTERSECTION WITH THE ITCZ. 24-H SFC PRES
TENDENCIES SHOW A 1-2 MB DROP ACROSS THESE ISLANDS. IN
ADDITION...SOUNDINGS FROM BARBADOS INDICATE A WEAK WAVE PASSAGE
BETWEEN 00Z-12Z TODAY WITH THE 600-925 MB FLOW SHIFTING
FROM THE NE TO DUE E.

TROPICAL WAVE IN THE CENTRAL CARIBBEAN AND SW N ATLANTIC IS
TILTED FROM 24N68W THROUGH 12N70W TO INLAND OVER SOUTH AMERICA.
THE GREATEST SIGNAL ASSOCIATED WITH THIS WAVE IS NEAR THE NRN
PART JUST E OF THE BAHAMAS. SATELLITE IMAGERY AND SHIP OBS IN
THE REGION CLEARLY DISPLAY SOME LOW-LEVEL TURNING. SCATTERED
SHOWERS AND ISOLATED TSTM LIE ALONG AND JUST TO THE E OF THE
AXIS FROM 20N-23N BETWEEN 66W-70W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N16W 10N30W 13N45W 10N55W 12N59W.
SCATTERED MODERATE CONVECTION...ASSOCIATED WITH THE NEXT
TROPICAL WAVE...IS LOCATED WITHIN 210 NM EITHER SIDE OF THE AXIS
E OF 20W. SCATTERED MODERATE IS ALIGNED WITHIN 90 NM S OF THE
AXIS BETWEEN 30W-39W NEAR THE BASE OF THE TROPICAL WAVE ALONG
35W. SCATTERED MODERATE AND ISOLATED STRONG IS LOCATED S OF THE
AXIS FROM 7N-9N W OF 50W.

...DISCUSSION...
GULF OF MEXICO...
SFC TROUGHING LIES ACROSS MOST OF THE N GULF ASSOCIATED WITH AN
AREA OF LOW PRES OFF THE CAROLINA COASTLINE AND A TRAILING
BOUNDARY WHICH EXTENDS W ACROSS THE SRN STATES. AN ILL-DEFINED
PREFRONTAL TROUGH LIES AHEAD OF THE FRONT IN THE N CENTRAL GULF
FROM 28N86W TO SW LOUISIANA. LIFT ALONG THESE BOUNDARIES IN
COMBINATION WITH DIFFLUENCE ALOFT OVER FLORIDA AND THE NE GULF
ARE TRIGGERING SCATTERED SHOWERS AND TSTMS FROM 27N-29N E OF
90W. ALTHOUGH IR IMAGERY AND LIGHTNING DATA SHOWS A GENERAL
DECREASE IN THE TSTM ACTIVITY OVER THE PAST SEVERAL HOURS...A
FAIR AMOUNT OF ACTIVITY IS EXPECTED TO PERSIST OVER THE NEXT
COUPLE OF DAYS AS THE PATTERN HOLDS. EXTENSIVE NELY UPPER
FLOW...ON THE W PERIPHERY OF A RIDGE OVER S TEXAS...IS ADVECTING
DEBRIS HIGH CLOUDINESS ACROSS MUCH OF THE REMAINDER OF THE GULF.
A WEAK 1017 MB SFC HIGH IS LOCATED TO THE SE OF THE TROUGHING
NEAR 24N84W. OVERALL SFC WINDS ARE ANTICYCLONIC AROUND THE WEAK
HIGH...ACCELERATING A BIT IN THE NE GULF NEAR THE FRONT.

CARIBBEAN...
CONDITIONS ACROSS THE MAJORITY OF THE CARIBBEAN SEA ARE TRANQUIL
THIS AFTERNOON IN RESPONSE TO ABUNDANT DRY STABLE AIR ALOFT. THE
ONLY AREA OF ORGANIZED ACTIVITY IS OVER THE ERN-MOST CARIB  AND
LESSER ANTILLES ASSOCIATED WITH THE TROPICAL WAVE ALONG
59W/60W...SEE ABOVE. ISOLATED SHOWERS AND TSTMS ARE LOCATED
BETWEEN JAMAICA AND 85W...ASSOCIATED WITH UPPER INSTABILITY
ROTATING AROUND INVERTED TROUGHING WHICH RUNS FROM COLOMBIA TO
NW CUBA. THIS MORNING'S QSCAT PASS SHOWS MAX WINDS NEAR 20 KT IN
THE CENTRAL CARIB. ELY TRADES ARE ANTICIPATED TO INCREASE IN THE
E AND CENTRAL CARIB OVER THE NEXT FEW DAYS AS THE ATLC RIDGE
STRENGTHENS.

ATLANTIC...
SEE SPECIAL FEATURES FOR INFORMATION ON TROPICAL STORM CHANTAL
AND THE 1010 MB LOW PRES SYSTEM IN THE TROPICAL ATLANTIC. VERY
AMPLIFIED PATTERN IN PLACE OVER THE N ATLANTIC WILL HELP START
THE EXTRATROPICAL TRANSITION PROCESS FOR CHANTAL OVER THE NEXT
DAY OR SO. BROAD COMPLEX TROUGH OVER THE NW ATLANTIC WITH FIRST
NEGATIVELY TILTED SHORTWAVE EXTENDING FROM NEW ENGLAND SEWD
THROUGH 37N64W TO 33N63W. UPPER LEVEL DIFFLUENCE E OF THE TROUGH
AXIS IS ALLOWING SCATTERED SHOWERS TO PERSIST TO THE SSE OF THE
TROPICAL STORM. A SECOND POTENT SHORTWAVE TROUGH IS SWINGING IN
FROM THE NW CUTTING ACROSS THE MID-ATLANTIC STATES. THIS
SHORTWAVE IS SUPPORTING A COLD FRONT WHICH EXTENDS FROM A 1008
MB LOW NEAR 34N75W TO THE NE FLORIDA COAST. SWLY FLOW/DIFFLUENCE
ALOFT AHEAD OF THE TROUGH AXIS IS GENERATING SCATTERED SHOWERS
AND TSTMS N OF 28N BETWEEN 70W-79W.

FURTHER S...AN ELONGATED RIDGE AXIS FROM 32N57W SWWD TO
THE WRN BAHAMAS WITH SOME MODERATE SUBSIDENCE NOTED S OF THE
RIDGE. CYCLONIC CIRCULATION NEAR 32N51W MOVING WWD 10 KT HAS
ASSOCIATED SHEAR AXIS EXTENDING SWWD TO A SMALL CYCLONIC
CIRCULATION NEAR 20N65W. ANTICYCLONES NEAR 16N51W AND 26N28W
AND ASSOCIATED FLOW PREVAIL OVER THE REMAINDER OF THE ATLANTIC
WITH DEEP EASTERLY FLOW IN PLACE ABOVE THE AREA. UW CIMSS SAL
ANALYSIS AND THE HAZY APPEARANCE ON VIS IMAGES INDICATE THAT THE
SAHARAN DUST HAS SPREAD TO ABOUT 50W THOUGH THE COVERAGE IS NOT
AS EXTENSIVE AS PREVIOUS DAYS. AT THE SURFACE...DRY STABLE AIR E
OF 60W AND A SURFACE RIDGE ANCHORED BY A 1027 MB HIGH WELL N OF
THE REGION NEAR 40N39W DOMINATE THE ATLC GIVING THE AREA FAIR
CONDITIONS TODAY.

$$
CANGIALOSI






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