[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 271755
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU AUG 27 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
1715 UTC.

...SPECIAL FEATURES...

TROPICAL STORM DANNY IS CENTERED NEAR 27.5N 73.1W AT 27/1500 UTC
OR ABOUT 280 NM NE OF NASSAU AND ABOUT 480 NM S-SE OF CAPE
HATTERAS NORTH CAROLINA MOVING NW OR 310 DEG AT 11 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED WIND
SPEED IS 50 KT WITH GUSTS TO 60 KT. SLOW STRENGTHENING IS
POSSIBLE DURING THE NEXT COUPLE OF DAYS...AND THE FORECAST CALLS
FOR DANNY TO BECOME A HURRICANE IN ABOUT 48 HOURS BEFORE START
TO LOSE TROPICAL CHARACTERISTICS. SCATTERED TO NUMEROUS MODERATE
TO STRONG CONVECTION IS FROM 26N-29N BETWEEN 68W-72W. SEE LATEST
NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT5/WTNT25
KNHC FOR MORE DETAILS. INTERESTS FROM THE CAROLINAS NORTHWARD TO
NEW ENGLAND SHOULD MONITOR THE PROGRESS OF DANNY. A TROPICAL
STORM WATCH MAY BE REQUIRED FOR PORTIONS OF THIS AREA LATER
TODAY.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 26W S OF 19N MOVING W NEAR 15 KT. THIS
WAVE COINCIDES WITH A BROAD AREA OF LOW-LEVEL CYCLONIC CURVATURE
NEAR 10.5N26.0W. THE CIMSS WAVETRACK GUIDANCE DEPICTS A MAXIMUM
AREA OF 850 MB VORTICITY IN THE VICINITY OF THE WAVE AXIS AND
ACROSS THE CAPE VERDE ISLANDS. THE ASSOCIATED SHOWER ACTIVITY
HAS BECOME A LITTLE BETTER ORGANIZED DURING THE MORNING HOURS
AND ADDITIONAL SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE OVER
THE NEXT COUPLE OF DAYS. SATELLITE IMAGERY SHOWS AN AREA OF
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION JUST AHEAD OF
THE WAVE AXIS FROM 8N-12N BETWEEN 28W-32W. THIS CONVECTION IS
BEING ENHANCED BY UPPER LEVEL DIFFLUENCE ON THE SRN PERIPHERY OF
AN ERN TROPICAL ATLC UPPER LEVEL ANTICYCLONIC CIRCULATION
CENTERED NEAR 19N29W.

A SECOND TROPICAL WAVE IS ALONG 46W S OF 20N MOVING W NEAR 15
KT. ONLY A FEW SHOWERS ARE NOTED NEAR THE INTERSECTION OF THE
WAVE AXIS AND THE ITCZ. AN UPPER LEVEL LOW IS CENTERED N OF THE
THIS FEATURE AND IS HELPING TO INDUCE SCATTERED SHOWERS NEAR THE
NORTHERN END OF THIS WAVE.

A THIRD TROPICAL WAVE IS ALONG 77W S OF 19N MOVING W NEAR 10 KT.
WAVE REMAINS WITHIN AN AREA OF MAXIMUM DEEP LAYER MOISTURE AS
OBSERVED ON THE TOTAL PRECIPITABLE WATER IMAGERY...HOWEVER
DRY...SUBSIDENT NELY FLOW ALOFT IS OVER THE CENTRAL CARIBBEAN
AND THUS INHIBITING ANY DEEP CONVECTION OR SHOWER ACTIVITY.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 10N15W 12N23W 10N35W 12N44W
11N48W 10N61W. OUTSIDE OF THE CONVECTION ASSOCIATED WITH THE
TROPICAL WAVES...SCATTERED MODERATE CONVECTION IS ALONG THE W
AFRICA COAST FROM 8N-13N BETWEEN 13W-17W. ISOLATED TO SCATTERED
MODERATE CONVECTION IS WITHIN 90 NM N OF AXIS BETWEEN 48W AND
53W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 1500...A SURFACE TROUGH IS ANALYZED ACROSS THE ERN GULF
EXTENDING FROM 29N84W TO NEAR 25N86W. AN AREA OF SHOWERS WITH
EMBEDDED TSTMS IS MAINLY E OF THE TROUGH AXIS COVERING N OF 26N
AND E OF 85W. SIMILAR CONVECTION IS ALSO NOTED N OF 28N BETWEEN
86W AND 89W. THIS SURFACE TROUGH IS SUPPORTED BY AN UPPER LEVEL
LOW CENTERED OVER ERN LOUISIANA. AN UPPER LEVEL RIDGE COVERS THE
REMAINDER OF THE GULF ANCHORED BY AN UPPER LEVEL ANTICYCLONE
CENTERED OVER THE YUCATAN CHANNEL. BETWEEN THESE TWO UPPER LEVEL
FEATURES...A BAND OF MID/UPPER LEVEL MOISTURE IS OBSERVED UNDER
A PREVAILING SWLY FLOW ALOFT AND EXTENDS FROM E/CENTRAL MEXICO
TO THE NE GULF AND NRN FLORIDA. AT THE SURFACE...A WEAK RIDGE OF
HIGH PRESSURE IS FORECAST TO REMAIN ACROSS THE NORTHERN GULF
WATERS AHEAD OF THE NEXT FRONTAL BOUNDARY THAT IS EXPECTED TO
MOVE INTO THE N GULF SUN NIGHT. A WEAK SFC TROUGH IS OVER THE SW
PORTION OF THE GULF WITH ISOLATED SHOWERS.

CARIBBEAN SEA...
AN UPPER-LEVEL ANTICYCLONE CENTERED OVER THE YUCATAN CHANNEL
DOMINATES THE WESTERN CARIBBEAN AND MUCH OF CENTRAL AMERICA
WHILE UPPER LEVEL TROUGHING COVERS THE CENTRAL CARIBBEAN WITH AN
EMBEDDED UPPER-LEVEL LOW SITUATED NEAR 15N75W. THIS WEATHER
PATTERN ALOFT IS HELPING TO INDUCE SOME SHOWER ACTIVITY OVER THE
NW CARIBBEAN AND CENTRAL AMERICA. THE EASTERN CARIBBEAN IS UNDER
THE INFLUENCE OF ANOTHER RIDGE THAT IS PRODUCING MODERATE TO
STRONG SUBSIDENCE AND THE IMPLIED DRY AIR MASS. AS A RESULT...
ONLY SHALLOW TRADE WIND SHOWERS ARE NOTED ACROSS THE AREA.

ATLANTIC OCEAN...
ALL THE ATTENTION REMAINS FOCUSED ON TROPICAL STORM DANNY MOVING
SOMEWHAT ERRATICALLY TOWARD THE NORTHWEST OVER PORTIONS OF THE
SW NORTH ATLC. THE LOW-LEVEL CENTER OF DANNY REMAINS EXPOSED BUT
NOW IT IS CLOSER TO THE DEEP CONVECTION MAINLY LOCATED TO THE
EAST. SEE SPECIAL FEATURES FOR MORE DETAILS. AN UPPER-LEVEL
TROUGH EXTENDS NWD TO NEAR DANNY FROM THE UPPER- LEVEL LOW
LOCATED OVER THE CENTRAL CARIBBEAN WHILE UPPER RIDGING IS
LOCATED TO THE E AND W OF THE TROPICAL CYCLONE. THE REMAINDER OF
THE SW NORTH ATLC IS UNDER THE INFLUENCE OF THE RIDGE ANCHORED
OVER THE YUCATAN CHANNEL. AN UPPER LEVEL LOW IS SPINNING OVER
THE CENTRAL ATLC NEAR 28N48W GENERATING ISOLATED TO SCATTERED
SHOWERS. A WEAK SFC TROUGH IS ANALYZED IN THIS AREA ALONG
50W/51W. FARTHER TO THE EAST...A WEAKENING UPPER LEVEL TROUGH
WITH AXIS N OF 23N ALONG 37W IS PRODUCING A BAND OF CLOUDINESS
WITH ISOLATED SHOWERS. AT THE SURFACE...THE AZORES-BERMUDA HIGH
LOCATED NEAR 42N28W DOMINATES MOST OF THE E AND CENTRAL
ATLANTIC.

$$
GR/MH






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