[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 230036 AAA
TWDAT

TROPICAL WEATHER DISCUSSION...UPDATED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI MAY 22 2009

...UPDATED TO INCLUDE SPECIAL FEATURE SECTION...

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2245 UTC.

...SPECIAL FEATURE...
A 1007 MB SURFACE LOW IS LOCATED NEAR 27N87W...OR ABOUT 175 NM
SOUTH OF PENSACOLA FLORIDA. A SURFACE TROUGH EXTENDS FROM THE
SURFACE LOW TO THE N YUCATAN PENINSULA NEAR 21N87W. LOW LEVEL
CONVERGENCE NEAR THE SURFACE LOW AND SURFACE TROUGH...AS WELL AS
UPPER LEVEL DIFFLUENCE E OF AN ASSOCIATED UPPER LOW NEAR
28N88W...ARE SUPPORTING NUMEROUS SHOWERS AND THUNDERSTORMS
ACROSS THE GULF N OF 23N E OF 89W....INCLUDING THE COASTAL
WATERS ACROSS THE N AND E GULF. THE TIGHT SURFACE PRESSURE
GRADIENT BETWEEN THE SURFACE LOW AND A SURFACE RIDGE OVER THE SE
CONUS IS SUPPORTING WIND SPEEDS OF 20 TO 25 KT AROUND THE LOW
ACROSS N PORTIONS OF THE MIDDLE GULF. THE SURFACE LOW IS
FORECAST TO MOVE NORTHWARD DURING THE NEXT DAY AND BE LOCATED
NEAR 30N89W AS A 1008 MB SURFACE LOW AT 23/1800 UTC. ADDITIONAL
DEVELOPMENT OF THIS SYSTEM IS POSSIBLE...AND A TROPICAL
DEPRESSION COULD FORM BEFORE THE LOW MOVES INLAND OVER THE
NORTHERN GULF COAST ON SATURDAY. IF NECESSARY...AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT WILL INVESTIGATE THE LOW
TOMORROW. THERE IS A MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
REGARDLESS OF DEVELOPMENT...HEAVY RAINS AND OCCASIONALLY GUSTY
WINDS ARE EXPECTED ALONG PORTIONS OF THE NORTHERN GULF COAST
TONIGHT AND SATURDAY. INTERESTS IN THIS AREA SHOULD MONITOR THE
PROGRESS OF THE SYSTEM.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 37W/38W SOUTH OF 7N MOVING WEST NEAR 15
KT. THIS WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER
MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS.
SATELLITE IMAGERY INDICATES CYCLONIC CIRCULATION IN THE MOTION
OF LOW LEVEL CLOUDS IN THE VICINITY OF THE WAVE. SUBSIDENCE IN
THE VICINITY OF A SURFACE RIDGE OVER THE E ATLC IS PREVENTING
THE DEVELOPMENT OF DEEP CONVECTION NEAR THIS WAVE...HOWEVER
SCATTERED SHOWERS ARE WITHIN 90 NM EITHER SIDE OF THE WAVE AXIS
FROM 1N-6N.

A TROPICAL WAVE IS ALONG 82W SOUTH OF 12N MOVING WEST NEAR 15
KT. THIS WAVE IS ALSO ASSOCIATED WITH A MAXIMUM IN DEEP LAYER
MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS.
LOW LEVEL CYCLONIC TURNING IS NOTED OVER THE SW CARIBBEAN DUE TO
THE COMBINATION OF THE WAVE AND A 1006 MB LOW E OF THE WAVE AXIS
OVER N COLOMBIA NEAR 8N74W. SCATTERED MODERATE CONVECTION IS
WITHIN 180 NM EITHER SIDE OF THE WAVE AXIS S OF 11N...INCLUDING
THE COASTS OF COSTA RICA AND PANAMA.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 6N10W 4N19W 1N28W CROSSING THE
EQUATOR NEAR 40W EXTENDING TO NE BRAZIL NEAR 1S46W. SCATTERED
MODERATE CONVECTION IS S OF 3N BETWEEN 6W-9W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS S OF 5N BETWEEN 14W-27W.
SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN 41W-46W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYER TROUGH IS PRESENT ACROSS THE GULF WITH AN UPPER
LEVEL LOW NEAR 28N88W AND AN ASSOCIATED 1007 MB SURFACE LOW NEAR
27N87W. NUMEROUS SHOWERS AND THUNDERSTORMS...AS WELL AS STRONGER
WINDS...ARE ASSOCIATED WITH THE SURFACE LOW. THIS SYSTEM IS
DISCUSSED IN THE SPECIAL FEATURE SECTION ABOVE. THE WINDS AROUND
THE LOW ARE FORECAST TO BECOME LIGHTER LATE THIS WEEKEND AS THE
PRESSURE GRADIENT AROUND THE LOW RELAXES. ACROSS THE W
GULF...SUBSIDENCE ASSOCIATED WITH NORTHWESTERLY FLOW ALOFT IS
SUPPORTING GENERALLY FAIR WEATHER CONDITIONS...WITH UPPER LEVEL
MOISTURE AND HIGH LEVEL CLOUDS STREAMING SOUTHEASTWARD. NW TO N
WINDS UP TO 20 KT ARE OCCURRING ACROSS PORTIONS OF THE NW GULF.
ADDITIONALLY...RECENT VISIBLE SATELLITE IMAGERY INDICATES THAT
AN AREA OF SMOKE ENTRAINED WITHIN THE LOW LEVEL SOUTHWESTERLY
FLOW AROUND THE AFOREMENTIONED LOW IS DRIFTING NORTHEASTWARD
FROM THE N YUCATAN PENINSULA ACROSS THE SE GULF...POTENTIALLY
REDUCING VISIBILITIES.

CARIBBEAN SEA...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS PERSIST ACROSS THE
E CARIBBEAN FROM 14N-18N BETWEEN 64W-71W. THIS ACTIVITY IS BEING
SUPPORTED BY UPPER LEVEL DIVERGENCE IN MOIST SOUTHWESTERLY FLOW
ALOFT BETWEEN AN UPPER LEVEL TROUGH OVER THE W CARIBBEAN AND
GULF OF MEXICO...AND AN UPPER LEVEL RIDGE ACROSS THE E CARIBBEAN
AND SW NORTH ATLC. THE UPPER LEVEL DIVERGENCE AND ASSOCIATED
SHOWER AND THUNDERSTORM ACTIVITY ARE CURRENTLY WEAKENING.
HOWEVER...ADDITIONAL SHOWERS AND THUNDERSTORMS COULD AFFECT
NORTHERN PORTIONS OF THE CARIBBEAN DURING THE NEXT COUPLE OF
DAYS WITH THE UPPER TROUGH AND ASSOCIATED ATMOSPHERIC
INSTABILITY PERSISTING OVER THE CARIBBEAN.
ADDITIONALLY...ATMOSPHERIC INSTABILITY NEAR THE UPPER TROUGH IS
RESULTING IN SCATTERED SHOWERS AND THUNDERSTORMS OVER
CUBA...HISPANIOLA...PUERTO RICO...AND NEARBY COASTAL WATERS...AS
WELL AS OVER THE W CARIBBEAN FROM 14N-19N BETWEEN 77W-86W. UPPER
LEVEL MOISTURE AND HIGH LEVEL CLOUDS ARE STREAMING GENERALLY
EASTWARD ACROSS THE CARIBBEAN. MEANWHILE...THE SURFACE PRESSURE
GRADIENT S OF A SURFACE RIDGE OVER THE CENTRAL ATLC IS
MAINTAINING E TO SE WINDS UP TO 20 KT ACROSS PORTIONS OF THE E
CARIBBEAN. ADDITIONALLY...A TROPICAL WAVE IS OVER THE SW
CARIBBEAN WITH SCATTERED MODERATE CONVECTION AFFECTING THE
COASTS OF COSTA RICA AND PANAMA. PLEASE SEE ABOVE FOR FURTHER
INFORMATION ON THIS TROPICAL WAVE.

ATLANTIC OCEAN...
SCATTERED SHOWERS AND THUNDERSTORMS ARE OCCURRING S OF 30N W OF
74W INCLUDING THE NW BAHAMAS AND THE COAST OF FLORIDA...AS WELL
AS S OF 24N BETWEEN 64W-74W INCLUDING CUBA...HISPANIOLA...PUERTO
RICO...AND THE SE BAHAMAS. THIS ACTIVITY IS BEING SUPPORTED BY
UPPER LEVEL DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT BETWEEN
AN UPPER LEVEL TROUGH OVER THE GULF OF MEXICO AND W CARIBBEAN...
AND AN UPPER LEVEL RIDGE ACROSS THE SW NORTH ATLC AND E
CARIBBEAN. ATMOSPHERIC INSTABILITY NEAR THE UPPER LEVEL TROUGH
IS ALSO SUPPORTING THE SHOWER AND THUNDERSTORM ACTIVITY. FARTHER
TO THE E...AN UPPER LEVEL TROUGH IS PRESENT WITH AN AXIS
EXTENDING FROM AN UPPER LEVEL LOW NEAR 31N55W TO 27N52W TO
25N50W. ATMOSPHERIC INSTABILITY NEAR THE UPPER LEVEL LOW AND
TROUGH...AS WELL AS UPPER LEVEL DIFFLUENCE IN MOIST
SOUTHWESTERLY FLOW ALOFT...ARE SUPPORTING SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS N OF 24N BETWEEN 43W-55W. THIS ACTIVITY
IS ALSO BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE
TROUGH EXTENDING FROM 31N51W TO A 1016 MB SURFACE LOW NEAR
27N57W CONTINUING TO 22N62W TO 21N68W. THIS LOW LEVEL
CONVERGENCE IS ALSO SUPPORTING SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS FROM 17N-22N BETWEEN 57W-65W. DURING THE NEXT
DAY...THE 1016 MB SURFACE LOW IS FORECAST TO DISSIPATE. ACROSS
THE E ATLC...A SURFACE RIDGE IS PRESENT WHERE MAINLY ZONAL FLOW
ALOFT IS OCCURRING AND FAIR WEATHER CONDITIONS PERSIST.
HOWEVER...AN UPPER LEVEL TROUGH IS PRESENT N OF 27N E OF 18W
WITH AN ASSOCIATED SURFACE TROUGH EXTENDING FROM 27N17W TO THE
CANARY ISLANDS NEAR 29N14W TO 32N10W TO N OF THE DISCUSSION
AREA. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS
WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. ACROSS THE
TROPICAL ATLC...AN UPPER LEVEL RIDGE IS S OF 11N E OF 41W WITH
AN UPPER LEVEL HIGH NEAR 7N28W. UPPER LEVEL DIVERGENCE
ASSOCIATED WITH THE UPPER LEVEL HIGH AND UPPER LEVEL RIDGE IS
ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ.

$$
COHEN




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