[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 091754
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN AUG 09 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND 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
1730 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 21W FROM 08N TO 17N MOVING W 10-15 KT.
ASSOCIATED LOW PRES 1010 MB IS LOCATED ALONG THE WAVE AXIS NEAR
13N. LATEST VISIBLE SATELLITE IMAGERY INDICATED A WELL DEFINED
LOW/MID LEVEL CYCLONIC CIRCULATION WITH A CLUSTER OF MODERATE TO
STRONG CONVECTION FLARING UP NEAR THE LOW LEVEL CIRCULATION...AND
AN ADDITIONAL BAND OF SCATTERED MODERATE CONVECTION WITHIN 90 NM
EITHER SIDE OF A LINE THROUGH 12N21W TO 09N25W. THERE IS A
MEDIUM PROBABILITY OF TROPICAL CYCLONE FORMATION WITH THIS WAVE
AND LOW OVER THE NEXT 48 HOURS. REFER TO THE TROPICAL WEATHER
OUTLOOK UNDER AWIPS/WMO HEADERS MIATWOAT/ABNT20 KNHC FOR
ADDITIONAL DETAILS.

TROPICAL WAVE IS TILTED NW TO SE FROM 20N42W TO 06N37W MOVING W
NEAR 15 KT. THE AXIS OF THE WAVE IS ORIENTED WITHIN A MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. THERE IS NO DEEP
CONVECTION ASSOCIATED WITH THE WAVE...HOWEVER SOME TURNING WAS
NOTED IN THE FIELD OF STRATOCUMULUS COMPRISING THE NORTHERN
EXTENT OF THE WAVE.

TROPICAL WAVE IS ALONG 47W/48W S OF 15N MOVING W NEAR 12 KT.
WAVE IS ALONG THE TRAILING EDGE OF A MOISTURE MAXIMUM OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY WITH NO ASSOCIATED DEEP
CONVECTION. THE WAVE IS OF LOW AMPLITUDE AND MAY BECOME ABSORBED
INTO THE LARGER CIRCULATION COMPRISING THE WAVE ABOVE.

TROPICAL WAVE IS ALONG 65W S OF 16N MOVING W NEAR 20 KT. THE
WAVE IS EMBEDDED WITHIN AN AREA OF MODERATE EASTERLY TRADES
OVER THE E CARIBBEAN WHICH IS PARTIALLY MASKING THE WAVE
SIGNATURE AND ANY SHOWERS/CONVECTION IS MORE ASSOCIATED WITH THE
ITCZ THAN THE WAVE ITSELF.

TROPICAL WAVE IS ALONG 86W S OF 20N MOVING W NEAR 17 KT. WAVE
REMAINS ALONG THE TRAILING EDGE OF A MOISTURE MAXIMUM OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY AND IS EMBEDDED IN RATHER
DRY STABLE AIR WITH NO ASSOCIATED DEEP CONVECTION.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 13N22W 9N35W 10N46W 14N55W
11N64W. A SURFACE TROUGH EXTENDING FROM 18N56W TO 10N55W WITH
CLUSTERS OF SCATTERED MODERATE ISOLATED STRONG CONVECTION W OF
THE TROUGH AXIS WITHIN 60-75 NM OF LINE FROM 16N56W TO
14N58W...THEN ACROSS THE SOUTHERN WINDWARD ISLANDS NEAR 13N62W.
CLUSTERS OF SCATTERED MODERATE TO ISOLATED STRONG CONVECTION ARE
WITHIN 120 NM S OF THE ITCZ BETWEEN 35W-43W.

...DISCUSSION...

GULF OF MEXICO...
AMPLIFIED PATTERN IN PLACE OVER THE CONUS WITH AN UPPER
RIDGE/ANTICYCLONE ANCHORED OVER SOUTH CAROLINA WITH AN EXTENSION
OF THE RIDGE INTO THE GULF OF MEXICO TO NEAR 22N94W. SURGE OF
DRY AIR ALOFT WAS SWEEPING SWD ACROSS THE NW ATLANTIC...FLORIDA
AND THE FAR E GULF CAPPING THUNDERSTORM DEVELOPMENT OVER FLORIDA
EXCEPT IN AREAS OF SEABREEZE CONVERGENCE. ON THE BACKSIDE OF THE
RIDGE AND EAST OF A TROUGH OVER MEXICO SOUTHERLY FLOW ALOFT WAS
ADVECTING SIGNIFICANT DEEP LAYERED MOISTURE NWD TOWARD THE TEXAS
AND LOUISIANA COASTS. 12Z RAOBS FROM THE AREA INDICATED
PRECIPITABLE WATER VALUES OF 2 TO 2.25 INCHES. SCATTERED
THUNDERSTORMS WERE POPPING UP OVER THE NW GULF AND THE ADJACENT
COASTAL AREAS OF TEXAS AND LOUISIANA WITH DAYTIME HEATING. A
MORE CONCENTRATED AREA OF SCATTERED STRONG THUNDERSTORMS WAS
OCCURRING OVER THE FAR SW GULF AND ALONG THE COAST OF MEXICO
FROM VERACRUZ TO TAMPICO.

CARIBBEAN SEA...
THE PERIPHERY OF AN UPPER RIDGE OVER THE NW ATLC AND E GULF OF
MEXICO WAS RETREATING AWAY FROM THE NW CARIBBEAN. IN ITS WAKE
AN UPPER LEVEL TROUGH EXTENDING FROM THE WINDWARD PASSAGE TO
JUST OFF THE COAST OF NICARAGUA WAS ADVANCING WESTWARD AT 10-15
KT. VERY DRY AIR ALOFT WAS NOTED WITHIN 120 NM OF THE TROUGH
AXIS AND WAS SPREADING WESTWARD OVER PORTIONS OF HONDURAS AND
NICARAGUA. AN UPPER LEVEL RIDGE AXIS EXTENDED FROM THE NORTHERN
LEEWARD ISLANDS TO 14N76W. DIFFLUENT SOUTH AND SOUTHEASTERLY
FLOW OVER THE CARIBBEAN S OF THE RIDGE AXIS WAS AIDING IN THE
DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE
SOUTHERN WINDWARD ISLANDS AND NEAR THE ABC ISLANDS. THIS
ACTIVITY APPEARED TO BE ALIGNED WITH AN EXTENSION OF THE ITCZ
FROM THE ATLANTIC. A MORE CONCENTRATED AREA OF SCATTERED STRONG
THUNDERSTORMS WAS OCCURRING OVER THE FAR SW CARIBBEAN WITHIN 90
NM OF THE COAST OF PANAMA AND COSTA RICA.

ATLANTIC OCEAN...
AN UPPER RIDGE/ANTICYCLONE OVER SOUTH CAROLINA GOVERNED THE
PATTERN OVER THE FAR NW PORTION OF THE SUBTROPICAL ATLC WITH DRY
AIR ALOFT SWEEPING SW ACROSS THE REGION SUPPRESSING THUNDERSTORM
ACTIVITY EXCEPT IN AREAS OF SEABREEZE/FAVORED CONVERGENCE.
FURTHER E...A NARROW UPPER TROUGH EXTENDED FROM 27N63W ACROSS
THE WINDWARD PASSAGE INTO THE WEST-CENTRAL CARIBBEAN. A LARGE
AREA OF UPPER LEVEL DIFFLUENT FLOW EXISTED BETWEEN THE RIDGE AND
TROUGH AND SUPPORTED THE GENERATION OF SCATTERED SHOWERS AND
THUNDERSTORMS WITHIN 60-90 NM S OF A SURFACE TROUGH WHICH
EXTENDS FROM 31N62W TO 28N72W. AN UPPER LOW OVER THE CENTRAL
ATLC NEAR 32N45W IS BEGINNING TO SHEAR OUT TO THE NE OVER AN
AMPLIFIED RIDGE EXTENDING FROM 32N33W TO AN ANTICYCLONE NEAR
22N38W THEN CONTINUING SW TO NEAR 18N55W. A CHANNEL OF MODERATE
TO STRONG NORTHERLY WINDS AND DRY AIR ALOFT WAS SWEEPING SWD
BETWEEN THE RIDGE AND AN UPPER LEVEL LOW NEAR THE CANARY
ISLANDS. THIS FLOW MAY IMPACT THE POTENTIAL DEVELOPMENT OF THE
LOW PRESSURE AREA NEAR 13N21W/THE CAPE VERDE ISLANDS. THE
REMAINDER OF THE ATLC REMAINS TRANQUIL WITH A BROAD AREA OF
SAHARAN DUST COVERING MOST OF THE AREA E OF 75W.

$$
COBB



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