[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 272344
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT OCT 27 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURE...

AN AREA OF LOW PRESSURE...ANALYZED 1003 MB...IS CENTERED ABOUT
100 NM S OF HAITI NEAR 16N71W. THE LOW-LEVEL CIRCULATION IS
FAIRLY WELL DEFINED BUT REMAINS EXPOSED TO THE W OF A LARGE
CONVECTIVE MASS. BASED ON THIS ORGANIZATION...IT IS CLEAR THAT
THIS SYSTEM IS FEELING SOME EFFECTS OF WLY SHEAR TO THE S OF AN
UPPER LOW. CONVECTION HAS GENERALLY BEEN ON THE INCREASE THIS
EVENING...NOW NUMEROUS MODERATE/SCATTERED STRONG IN NATURE...TO
THE NE OF THE CENTER FROM 16N-18N BETWEEN 68W-71W. A LARGE
RATHER MESSY AREA OF SCATTERED MODERATE CONVECTION EXISTS
ELSEWHERE FROM 12N-19N BETWEEN 61W-74W...WHICH INCLUDES PUERTO
RICO...THE VIRGIN ISLANDS AND THE LESSER ANTILLES. METAR AND
BUOY DATA INDICATES THAT THIS LOW IS RATHER BROAD WITH MANY
STATIONS IN THE CENTRAL AND E CARIB REPORTING AN SLP LOWER THAN
1008 MB. ANY INCREASE IN ORGANIZATION COULD LEAD TO THE
FORMATION OF A TROPICAL DEPRESSION AND INTERESTS IN THE CENTRAL
AND NORTHWESTERN CARIBBEAN SEA SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE THE AREA ON SUNDAY...IF NECESSARY.

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 42W S OF 14N MOVING W 15 KT. THIS WAVE
HAS GENERALLY CHANGED LITTLE OVER THE PAST DAY OR TWO. A NARROW
BAND OF MOISTURE AND AREA OF LOW-LEVEL TURNING IS APPARENT ON
SATELLITE IMAGERY. THE NRN PORTION OF THE WAVE IS BEGINNING TO
TILT AS IT FEELS THE EFFECTS OF EXTENSIVE SWLY FLOW ASSOCIATED
WITH A DEEP LAYER TROUGH TO ITS NNW. SCATTERED SHOWERS AND
ISOLATED TSTMS ARE WITHIN 90 NM EITHER SIDE OF THE WAVE AXIS N
OF 8N.

TROPICAL WAVE IS ALONG 52W S OF 12N MOVING W 10-15 KT. NEARLY
ALL OF THE ASSOCIATED MOISTURE HAS BEEN ABSORBED BY THE DEEP
LAYER TROUGH TO THE N OF THE WAVE. THERE IS NOT MUCH EVIDENCE OF
ANY LEFT OVER TROPICAL PORTION...SO JUST EXTRAPOLATED THE
POSITION W SLIGHTLY.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 7N11W 5N23W 3N39W 3N51W. WIDELY
SCATTERED MODERATE CONVECTION IS WITHIN 150 NM EITHER SIDE OF
THE AXIS E OF 32W.

DISCUSSION...

GULF OF MEXICO...
A WEAKENING SLOW MOVING FRONT EXTENDS ACROSS CENTRAL FLORIDA
TOWARD THE YUCATAN CHANNEL ALONG 29N81W 27N84W 22N86W. LOW-LEVEL
CONVERGENCE NEAR THIS BOUNDARY ALONG WITH A SOMEWHAT DIFFLUENT
PATTERN ALOFT IS PRODUCING SCATTERED SHOWERS AND TSTMS ROUGHLY
WITHIN 120 NM AS NOTED IN MOSAIC DOPPLER RADAR AND LIGHTNING
DATA. THE TIGHTENED PRES GRADIENT BETWEEN THIS FRONT AND STRONG
HIGH PRES OVER THE UPPER PLAINS IS PRODUCING STRONG NELY WINDS
ACROSS THE CENTRAL AND E PORTIONS. THESE WINDS ARE EXPECTED TO
INCREASE FURTHER WITH GALE CONDITIONS FORECAST FOR THE SW GULF
IN ABOUT 30 HOURS. THE MAJORITY OF THE GULF...W OF 88W...IS
UNDER STRONG SUBSIDENCE ALONG AND TO THE E OF AN UPPER TROUGH
ALONG 97W/98W. A LOW-LEVEL SCATTERED STRATOCUMULUS DECK IS
EVIDENT ON THE LAST FEW VIS IMAGES OF THE EVENING ACROSS THE
CENTRAL AND W GULF SIGNALING THE COOLER STABLE AIRMASS IN PLACE.

CARIBBEAN SEA...
THE MAIN EVENT IN THE CARIBBEAN THIS EVENING IS THE LARGE AREA
OF LOW PRES SITUATED S OF HISPANIOLA. FOR DETAILS SEE THE
SPECIAL FEATURE SECTION ABOVE. ANOTHER LOW PRES TROUGH IS
LOCATED IN THE NW CARIB ANALYZED FROM 21N86W TO 15N81W. VISIBLE
IMAGERY SHOWS LOW-LEVEL TURNING CONCENTRATED NEAR 17N84W. IR
IMAGERY AND LIGHTNING DATA REVEAL A FAIR AMOUNT OF SHOWERS AND
TSTMS WITHIN 120 NM OF THE AXIS BUT NOT MUCH ORGANIZATION TO
THIS ACTIVITY. ADDITIONAL DEVELOPMENT...IF ANY...SHOULD BE SLOW
TO OCCUR. A PATCH OF SCATTERED MODERATE CONVECTION IS LOCATED
FARTHER S IN THE SW CARIB FROM 11N-14N BETWEEN 81W-83W. THE
REMAINDER OF THE AREA...ROUGHLY N OF 16N BETWEEN 70W-79W...IS
UNDER A WEDGE OF DRY MID AND UPPER LEVEL AIR IN A CONFLUENT ZONE
TO THE S OF AN UPPER LOW OVER HAITI.

ATLANTIC...
STRONG HIGH PRESSURE DOMINATES THE WESTERN ATLANTIC ANCHORED BY
A PAIR OF 1031 MB CENTERS IN THE NORTH ATLANTIC. THE TIGHT PRES
GRADIENT BETWEEN THIS RIDGING AND A LARGE LOW PRES SYSTEM IN THE
CARIB IS GENERATING AN AREA OF 20-30 KT NE TO E WINDS S OF 26N
BETWEEN 63W AND 78W. THERE ARE LOW-LEVEL MOISTURE STREAMS
STEERED BY THIS FLOW BUT THE LARGE AREA OF DRY AIR IN THE MID
AND UPPER LEVELS IS PREVENTING THE FORMATION OF DEEP MOISTURE IN
THIS REGION. AN UPPER LOW OVER HAITI IS SHEARING THE LOW PRES
SYSTEM IN THE CARIB AND SPREADING DEBRIS MOISTURE INTO THE
TROPICAL ATLC ROUGHLY S OF 22N W OF 58W. FARTHER E...A LARGE
DEEP LAYER TROUGH DOMINATES THE CENTRAL ATLC WITH THE MAIN LOW
CENTERED NEAR 32N48W...ANALYZED 1010 MB AT THE SFC. A COLD FRONT
STRETCHES SW FROM THIS SYSTEM ALONG 32N47W 28N51W 29N63W.
ANOTHER SFC LOW IS LOCATED TO THE SE OF THE MAIN ONE NEAR 28N45W
ESTIMATED TO BE 1009 MB. THERE ARE ONLY ISOLATED SHOWERS AND
TSTMS NEAR THE LOWS...WITH MORE SCATTERED ACTIVITY TO THE EAST
GENERALLY N OF 25N BETWEEN 36W-42W IN AN UPPER DIFFLUENT AREA.
THE E ATLC IS RATHER TRANQUIL UNDER THE INFLUENCE OF SFC RIDGING
EXTENDING SWD FROM HIGH PRES E OF THE AZORES AND AN AMPLIFIED
RIDGE/TROUGH PATTERN. THERE IS SOME MID-HIGH LEVEL CLOUDINESS
EMBEDDED ON THE UPWARD SIDE OF THE RIDGE BUT MOST OF THIS DRIES
OUT E OF 25W.

$$
CANGIALOSI





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