[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 141040
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT TUE JUL 14 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1045 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 33W/34W S OF 18N MOVING W NEAR 20 KT.
THIS WAVE COINCIDES WITH A LOW AMPLITUDE MAXIMUM IN DEEP LAYER
MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM
CIMSS. SATELLITE-DERIVED WINDS INDICATE CYCLONIC CURVATURE IN
THE FLOW WITHIN THE 800-600 MB LAYER. THE QUIKSCAT PASS AROUND
13/2015 UTC INDICATED E WINDS AT 10-15 KT AHEAD OF THE WAVE
FOLLOWED BY E TO SE WINDS AT 15-20 KT BEHIND THE WAVE. THIS WAVE
IS ASSOCIATED WITH SCATTERED MODERATE CONVECTION FROM 9N-13N
BETWEEN 33W-37W.

A TROPICAL WAVE IS E OF THE LESSER ANTILLES AND EXTENDS FROM
24N59W TO 14N58W TO 6N54W MOVING W NEAR 20 KT. THE STRONG LOW
LEVEL EASTERLY JET FOLLOWING THE N PORTION OF THE WAVE IS
CONTRIBUTING TO THE NW-SE TILT OF THE WAVE. A WELL-DEFINED AND
HIGHLY-AMPLIFIED INVERTED-V PATTERN IS EVIDENT IN THE COVERAGE
OF LOW-LEVEL CLOUDS BASED ON RECENT SATELLITE IMAGERY...
COINCIDING WITH A MAXIMUM IN TOTAL PRECIPITABLE WATER. THE
RELATIVELY SHORT WAVELENGTH OF THE TROPICAL WAVE IS CURRENTLY
PRECLUDING AN EVEN FASTER WESTWARD WAVE MOTION. THE WAVE IS
LEADING ABUNDANT DRY LOW/MID-LEVEL SAHARAN AIR. THIS IS
CONTRIBUTING TO A DENSITY DIFFERENCE SUFFICIENT TO PROVIDE LOW
LEVEL ATMOSPHERIC LIFT SUPPORTING RECENT DEVELOPMENT OF
SCATTERED MODERATE CONVECTION ALONG AND WITHIN 60 NM E OF THE
WAVE AXIS. THIS IS PARTICULARLY THE CASE N OF 16N...WHICH IS IN
A ZONE OF UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE W
OF THE WAVE AND AN UPPER LEVEL TROUGH E OF THE WAVE. THE DRY AIR
IS LIKELY CONTRIBUTING TO STRONG DOWNDRAFTS AND GUSTY OUTFLOW
WINDS WITH THIS CONVECTION. THE GFS APPEARS TO HAVE A GOOD
HANDLE ON THIS FEATURE AND SHOWS IT MOVING INTO THE LESSER
ANTILLES DURING THE NEXT DAY.

A TROPICAL WAVE IS ALONG 92W S OF 19N MOVING W 15-20 KT. THE
WAVE POSITION IS MAINLY BASED ON A MOISTURE MAXIMUM IN TOTAL
PRECIPITABLE WATER AS FEW ADDITIONAL SIGNATURES ARE APPARENT IN
SATELLITE IMAGERY OR OBSERVATIONS. SCATTERED MODERATE CONVECTION
IS OVER SE MEXICO FROM 16N-18N BETWEEN 94W-96W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 12N16W 11N27W 10N38W 8N48W
8N61W. SCATTERED MODERATE TO STRONG CONVECTION IS FROM 7N-13N
BETWEEN 18W-22W. SCATTERED MODERATE CONVECTION IS FROM 7N-10N
BETWEEN 25W-32W. SCATTERED MODERATE CONVECTION IS ALSO FROM
8N-11N BETWEEN 42W-51W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL RIDGE EXTENDS SOUTHEASTWARD INTO THE GULF OF
MEXICO AND IS ASSOCIATED WITH A SURFACE RIDGE ALONG 26N AND A
1018 MB SURFACE HIGH NEAR 25N84W. GENERALLY FAIR WEATHER IS
PRESENT ACROSS THE GULF. ONE EXCEPTION IS OVER THE N CENTRAL
GULF...WHERE SCATTERED SHOWERS AND THUNDERSTORMS ARE PRESENT N
OF 28N BETWEEN 87W-90W. THIS ACTIVITY IS BEING SUPPORTED BY
ATMOSPHERIC LIFT ASSOCIATED WITH A WEAK SHORTWAVE TRANSLATING
SOUTHEASTWARD ON THE OUTER PERIPHERY OF THE AFOREMENTIONED UPPER
RIDGE. WINDS ARE LIGHT AND VARIABLE IN THE VICINITY OF THE
SURFACE RIDGE ACROSS THE N GULF...WITH ANTICYCLONIC FLOW AROUND
THE RIDGE SUPPORTING A BROAD SWATH OF E WINDS OF 10-15 KT ACROSS
THE S HALF OF THE GULF. LITTLE CHANGE IS EXPECTED OVER THE NEXT
DAY OR TWO AS BOTH THE UPPER AND SFC RIDGE REMAIN IN PLACE.

CARIBBEAN SEA...
FRESH TO STRONG TRADE WINDS ARE OCCURRING BETWEEN THE
SUBTROPICAL RIDGE OVER THE CENTRAL ATLC AND A BROAD TROUGH OVER
NORTHERN SOUTH AMERICA...WITH THE STRONGEST FLOW NEAR THE COAST
OF COLOMBIA. THESE WINDS WILL REMAIN STRONG OVER THE NEXT
SEVERAL DAYS AS THE SUBTROPICAL RIDGE REMAINS IN PLACE AND A
TROPICAL WAVE MOVES INTO THE AREA. IN FACT...GALE CONDITIONS ARE
FORECAST FOR THE LATTER HALF OF THIS WEEK...AS THE LOW LEVEL
FLOW STRENGTHENS ACROSS THE CARIBBEAN. ALOFT...INSTABILITY
ASSOCIATED WITH AN UPPER LEVEL LOW OVER THE N CENTRAL CARIBBEAN
CENTERED NEAR 18N79W IS RESULTING IN SCATTERED SHOWERS AND
THUNDERSTORMS N OF 16N BETWEEN 75W-82W INCLUDING PORTIONS OF
JAMAICA AND CUBA. DEEP LAYER DRY AIR IS RESULTING IN GENERALLY
FAIR WEATHER ACROSS THE E CARIBBEAN. A TROPICAL WAVE IS FORECAST
TO ENTER THE CARIBBEAN LATER TODAY. THE WAVE WILL  BE
ACCOMPANIED BY...AND FOLLOWED BY...STRONGER WINDS AND A STRONG
SURGE OF SAHARAN AIR...WHICH WILL LIMIT THE AREAL COVERAGE OF
DEEP CONVECTION NEAR THE WAVE...BUT WILL ALSO INCREASE THE
THREAT FOR STRONGER DOWNDRAFTS AND GUSTY OUTFLOW WINDS WITH ANY
CONVECTION THAT DEVELOPS.

ATLANTIC OCEAN...
DEEP LAYER MOISTURE IS COMBINING WITH UPPER LEVEL DIFFLUENCE IN
NORTHWESTERLY FLOW ALOFT TO RESULT IN SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE SW NORTH ATLC N OF 26N W OF
77W...INCLUDING PORTIONS OF THE NW BAHAMAS. ALSO...SCATTERED
SHOWERS AND ISOLATED TSTMS ARE N OF 24N BETWEEN 64W-71W. THIS
ACTIVITY IS BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A
SURFACE TROUGH EXTENDING FROM 28N67W TO 24N72W. THIS ACTIVITY IS
ALSO SUPPORTED BY ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN
UPPER TROUGH OVER THE SW NORTH ATLC. SUBSIDENCE AND GENERALLY
FAIR WEATHER ARE PRESENT ACROSS MUCH OF THE CENTRAL AND E ATLC
AROUND A BROAD SURFACE RIDGE WITH A 1031 MB HIGH NEAR 34N47W. A
SURFACE TROUGH FROM 31N32W TO 28N37W...THOUGH ASSOCIATED
CLOUDINESS AND SHOWERS ARE SHALLOW IN NATURE AND LIMITED TO
LOCATIONS WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. ACROSS
THE TROPICAL N ATLC...AN UPPER LEVEL RIDGE IS ALONG 14N E OF 39W
AND AN UPPER LEVEL HIGH IS CENTERED NEAR 14N30W...WITH
ASSOCIATED UPPER LEVEL DIVERGENCE ENHANCING THE CONVECTION NEAR
THE ITCZ.

$$
COHEN




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