[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 121054
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT WED SEP 12 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1045 UTC.

...SPECIAL FEATURE...
A SLOW MOVING AREA OF LOW PRESSURE CENTERED NEAR 13N43W OR ABOUT
1000 NM E OF THE LESSER ANTILLES CONTINUES TO ORGANIZE THIS
MORNING. THE MINIMUM PRES IS ANALYZED 1009 MB BASED ON BUOY
41041 LOCATED ABOUT 180 NM TO THE NW OF THE BROAD LOW. SATELLITE
IMAGERY SHOWS A CONSOLIDATING AND INCREASINGLY CIRCULAR MASS OF
CLOUDS ASSOCIATED WITH THIS SYSTEM. THE LOW-LEVEL CENTER IS
DIFFICULT TO PIN DOWN EXACTLY ALTHOUGH IT APPEARS TO BE
PARTIALLY TUCKED UNDER THE CLOUDINESS NEAR THE ERN EDGE OF
SCATTERED MODERATE CONVECTION FROM 12N-14N BETWEEN 43W-46W.
CONDITIONS APPEAR FAVORABLE FOR A TROPICAL DEPRESSION TO FORM
LATER TODAY OR TONIGHT AS THE SYSTEM MOVES WEST-NORTHWESTWARD AT
5-10 KT.

THE AREA OF LOW PRES IN THE NW GULF HAS BECOME BETTER ORGANIZED
OVERNIGHT. AS OF 09Z...THE LOW WAS ANALYZED NEAR 27N95W 1008
MB...WHICH IS 2 MB LOWER THAN OBSERVED 3 HOURS EARLIER AT 06Z.
IN ACCORDANCE...SHIP AND BUOY DATA DEPICT AN INCREASE IN WINDS
WITH THE HIGHEST REPORT NEAR 29 KT E OF THE CENTER. HOWEVER
...THIS REPORT SEEMS SUSPECT AND UNREPRESENTATIVE WHEN COMPARED
TO THE SURROUNDING 10-20 KT REPORTS. THESE OBSERVATIONS ALSO
REVEAL THAT THIS SYSTEM IS STILL AN ELONGATED N-S TROUGH
AXIS...THOUGH DOPPLER RADAR AND SATELLITE IMAGERY CLEARLY SHOW
AN IMPROVED AREA OF CYCLONIC TURNING TO THE CLOUD AND RAIN
ELEMENTS. PROBABLY THE CLEAREST INDICATION OF THE IMPROVED
STRUCTURE IS THE INCREASED SHOWER ACTIVITY WHICH HAS STARTED TO
SPREAD ACROSS EXTREME SE TEXAS. CURRENTLY SCATTERED SHOWERS AND
TSTMS ARE ROUGHLY WITHIN 90-120 NM OF THE LOW. ENVIRONMENTAL
CONDITIONS APPEAR TO BE CONDUCIVE FOR SOME DEVELOPMENT OF THIS
SYSTEM OVER THE NEXT DAY OR SO AS IT DRIFTS SLOWLY
WEST-NORTHWESTWARD.

...TROPICAL WAVES...

HIGH AMPLITUDE TROPICAL WAVE IN THE E ATLC ALONG 33W/34W S OF
23N MOVING W 15 KT. IN GENERAL...THIS WAVE HAS CHANGED LITTLE
OVER THE PAST COUPLE OF DAYS. THE STRUCTURE REMAINS WELL DEFINED
WITH A LARGE SHIELD OF CYCLONIC TURNING NOTED IN THE LOW TO MID
LEVEL CLOUD FIELD. IN ADDITION...THE UW-CIMSS TPW ANIMATION
REVEALS A LARGE WWD PROPAGATING SURGE OF MOISTENED AIR. AN
EARLIER QSCAT PASS DEPICTED A NEARLY CLOSED CIRCULATION ALONG
THE WAVE AXIS NEAR 15N AND EARLY MORNING VIS IMAGES SUGGEST THE
SAME...SO A LOW MAY BE ADDED ALONG THE WAVE ON THE NEXT SYNOPTIC
MAP. DESPITE THE FAIR STRUCTURE...DEEP MOISTURE IS MINIMAL WITH
ONLY A FEW SHOWERS AND TSTMS WITHIN 90 NM OF THE AXIS.
CONVECTION IS MORE SCATTERED IN NATURE NEAR THE INTERSECTION OF
THE ITCZ.

TROPICAL WAVE IS IN THE CENTRAL CARIB ALONG 72W S OF 20N MOVING
W 15-20 KT. THE INTERACTION WITH AN UPPER LOW HAS FUELED A
CONVECTIVE AREA OVER AND S OF HISPANIOLA FROM 17N-19N
BETWEEN 68W-72W. THIS ACTIVITY IS MOVING NNW STEERED BY THE
UPPER FLOW. IT IS NOTABLE THAT THE CURRENT POSITION HAS BEEN
ADJUSTED SLIGHTLY TO THE W IN AGREEMENT WITH A RATHER QUICK
NARROW MOISTURE SURGE EVIDENT ON THE CIMSS TPW ANIMATION...WHICH
WAS PARTICULARLY HELPFUL IN LOCATING THIS WAVE.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 9N16W 14N32W 14N41W 9N53W 9N62W.
WEAKENING SCATTERED MODERATE CONVECTION IS FROM 10N-14N BETWEEN
17W-22W LIKELY ASSOCIATED WITH THE NEXT TROPICAL WAVE. SCATTERED
MODERATE IS FROM 5N-8N BETWEEN 25W-30W AND NEAR THE BASE OF THE
E ATLC WAVE FROM 8N-11N BETWEEN 32W-36W. ISOLATED MODERATE IS
WITHIN 150 NM EITHER SIDE OF THE AXIS W OF 45W.

DISCUSSION...

THE GULF OF MEXICO...
THE TROUGH OF LOW PRES IN THE NW GULF HAS BECOME BETTER
ORGANIZED OVERNIGHT AND IS BEING CLOSELY MONITORED FOR
DEVELOPMENT. FOR DETAILS REFER TO THE SPECIAL FEATURE SECTION
ABOVE. ELSEWHERE...WATER VAPOR IMAGES AND THE CIMSS TPW PRODUCT
SHOW A MOISTENED STATE ACROSS THE ENTIRE AREA. A COMPLEX UPPER
PATTERN IS ONE OF THE PRIMARY CONTRIBUTING FACTORS. THE LARGE
SCALE UPPER FLOW IS MAINLY OUT OF THE N OR NE...HOWEVER THERE
ARE SMALL SYSTEMS PERTURBING THE FLOW WHICH HAS CAUSED SOME
DEEPENING OF THE AVAILABLE MOISTURE. ONE AREA OF SCATTERED
SHOWERS AND TSTMS IS OVER THE S CENTRAL GULF FROM 24N-27N
BETWEEN 84W-88W. THIS IS ASSOCIATED WITH A SMALL UPPER LOW IN
THAT AREA. SCATTERED SHOWERS AND TSTMS ARE OVER THE NE GULF AND
FL PANHANDLE N OF 28N E OF 88W AHEAD OF A SLOW MOVING FRONTAL
BOUNDARY WHICH IS ANALYZED JUST INLAND ACROSS THE GULF COAST
STATES. THIS BOUNDARY IS NOT EXPECTED TO PUSH VERY FAR...IF AT
ALL...INTO THE OFFSHORE WATERS TODAY BEFORE RETREATING AND
WEAKENING.

THE CARIBBEAN SEA...
A LARGE UPPER LEVEL LOW IS MOVING NWWARD...CURRENTLY SPINNING
OVER ERN CUBA. DIFFLUENCE BETWEEN THIS SYSTEM AND AN UPPER HIGH
IN THE TROPICAL ATLC...ALONG WITH LOW-LEVEL ENERGY ASSOCIATED
WITH A TROPICAL WAVE...IS SUPPORTING AN AREA OF SCATTERED
SHOWERS AND TSTMS OVER AND S OF HISPANIOLA FROM 17N-19N BETWEEN
68W-72W. A HIGH CLOUD DECK...DEBRIS MOISTURE...LIES ABOVE THE
REMAINDER OF THE AREA E OF 70W. INSTABILITY AND DIFFLUENCE
PARTIALLY ASSOCIATED WITH THE UPPER LOW IS ALSO HELPING TO
SUSTAIN SCATTERED SHOWERS AND TSTMS IN THE NW CARIB. NONE OF
THESE CLUSTERS ARE VERY DEEP OR ORGANIZED IN NATURE. MUCH DRIER
AIR LIES OVER THE CENTRAL CARIB WITHIN THE CIRCULATION OF THE
UPPER LOW BETWEEN 72W-79W. TRADE WINDS CONTINUE TO BE ON A SLOW
INCREASE...AS ADVERTISED...WITH 20-25 KT WINDS BLOWING OVER MUCH
OF THE CENTRAL AND E PORTIONS.

THE ATLANTIC OCEAN...
AN ORGANIZATION AREA OF LOW PRES LOCATED NEAR 13N43W IS BEING
CLOSELY MONITORED THIS MORNING. FOR DETAILS REFER TO THE SPECIAL
FEATURE SECTION ABOVE. ELSEWHERE AT THE SFC...NOT MUCH HAS
CHANGED OVER THE PAST DAY OR TWO. MODERATE SUBTROPICAL RIDGING
IS THE GENERAL THEME WITH A 1022 MB HIGH CENTER LOCATED NEAR
32N57W AND RIDGING EXTENDING SW INTO THE NE ATLC. THE PATTERN IS
WEAKENED IN THE CENTRAL ATLC...ALBEIT LESS SO THAT THE PAST FEW
DAYS...DUE TO A 1011 MB LOW AND TRAILING SFC TROUGH N OF THE
AREA. THIS HAS ALLOWED WINDS TO BE VERY LIGHT ACROSS THE
SUBTROPICAL CENTRAL ATLC WITH MORE TYPICAL MODERATE ELY TRADES
ELSEWHERE.

IN THE MID AND UPPER LEVELS...A DIFFLUENT PATTERN EXISTS ACROSS
THE W ATLC. THE CONTRIBUTING LARGE SCALE FEATURES CONSIST OF A
NWWD MOVING UPPER LOW CENTERED OVER ERN CUBA...AN UPPER HIGH
LOCATED NE OF BERMUDA AND AN ELONGATED SHORTWAVE WHICH ENTERS
THE AREA NEAR 32N38W AND EXTENDS FAIRLY FAR TO THE W ENDING NEAR
28N67W. THIS PATTERN IS HELPING TO SUSTAIN A LINEAR SWATH OF
CLOUDINESS WITH SCATTERED SHOWERS AND TSTMS CONFINED TO 23N-26N
BETWEEN 68W-77W. MUCH OF THE REMAINDER OF THE AREA IS DOMINATED
BY AN E-W RIDGE COVERING THE AREA E OF THE LESSER ANTILLES WITH
A MEAN AXIS ALONG 18N WITH SEVERAL EMBEDDED ANTICYCLONES. THIS
RIDGE AND A CONFLUENT PATTERN...TO THE S OF A LARGE UPPER LOW
NEAR SRN PORTUGAL...IS KEEPING WX CONDITIONS FAIRLY TRANQUIL
OUTSIDE OF THE AREAS OUTLINED ABOVE.

$$
CANGIALOSI




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