[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 151806 CCA
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI SEP 15 2006

CORRECTED TIME OF SATELLITE IMAGERY BASIS

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN
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...WEATHER OBSERVATIONS...RADAR...
AND METEOROLOGICAL ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...
HURRICANE GORDON WAS CENTERED NEAR 31.1N 53.3W AT 15/1500 UTC
MOVING NORTHEAST AT 6 KT. THIS MOTION IS EXPECTED TO CONTINUE
FOR THE NEXT 24 HOURS WITH A CONTINUED DECREASE IN FORWARD SPEED.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 973 MB. MAXIMUM SUSTAINED
WINDS ARE 85 KT WITH GUSTS TO 105 KT. GORDON REMAINS A CATEGORY
TWO HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE.  ADDITIONAL
WEAKENING IS FORECAST DURING THE NEXT 24 HOURS.SEE THE LATEST
NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22
KNHC FOR MORE DETAILS. INFRARED IMAGERY HAS SHOWN THAT THE CLOUD
TOPS NEAR THE CENTER OF GORDON HAVE WARMED A BIT THIS MORNING.
SCATTERED MODERATE CONVECTION NOW LIES FROM 30N-33N BETWEEN
52W-56W.

TROPICAL STORM HELENE WAS CENTERED NEAR 15.8N 41.4W AT 15/1500
UTC MOVING WEST-NORTHWEST AT 11 KT. THIS MOTION IS EXPECTED TO
CONTINUE DURING THE NEXT DAY OR TWO. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 1000 MB. MAXIMUM SUSTAINED WINDS ARE 50 KT WITH
GUSTS TO 60 KT. SOME STRENGTHENING IS FORECAST DURING THE NEXT
24 HOURS AND HELENE COULD BECOME A HURRICANE ON SATURDAY. SEE
THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. GOES AND METEOSAT
SATELLITE IMAGES INDICATE THAT THE CLOUD PATTERN IS BETTER
ORGANIZED AND IS MORE TYPICAL OF A TROPICAL STORM. THE
CONVECTION IS MORE CONCENTRATED NEAR THE CENTER...AND THERE IS A
WELL-DEFINED CYCLONICALLY CURVED BAND TO THE SOUTH WITH NUMEROUS
RAINBANDS ALL AROUND. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION EXISTS FROM 12N-19N BETWEEN 38W-45W.

...TROPICAL WAVES...
A TROPICAL WAVE HAS EMERGED OFF THE COAST OF AFRICA ALONG
19W/20W S OF 18N MOVING W NEAR 10 KT. THIS WAVE IS ACCOMPANIED
BY A 1013MB SURFACE LOW NEAR 14N. BROAD CYCLONIC CURVATURE IS
CLEARLY NOTED IN THE LOW TO MID CLOUD FIELD...AND IN THE
AVAILABLE SURFACE OBSERVATIONS. CLOUD TOPS ASSOCIATED WITH THIS
WAVE HAVE WARMED A FEW DEGREES OVER THE LAST FEW HOURS...THOUGH
SCATTERED MODERATE STILL EXISTS FROM 12N-18N BETWEEN 18W-23W.

TROPICAL WAVE IS ALONG 61W/62W S OF 15N MOVING W NEAR 15 KT.
THIS IS A LOW AMPLITUDE WAVE THAT IS NOT EASY TO IDENTIFY ON
SATELLITE IMAGERY. THERE HAS BEEN SOME SUBTLE TURNING IN THE
WIND FIELD IN THE SRN LESSER ANTILLES BUT SOME OF THIS MAY BE
DIURNALLY INDUCED.  DEEP CONVECTION REMAINS MINIMAL NEAR THIS
WAVE...ASIDE FROM SMALL CLUSTERS OF MODERATE CONVECTION NEAR THE
ITCZ AND NE S AMERICA BETWEEN 58W-63W.

TROPICAL WAVE IS ALONG 73W S OF 18N MOVING W 10 TO 15 KT. THIS
WAVE EXHIBITS AN INVERTED V PATTERN ON SATELLITE IMAGERY...WITH
ISOLATED AND TSTMS N OF 14N TO THE COAST OF HISPANIOLA
BETWEEN 68W-75W.

TROPICAL WAVE IS ALONG 81W/82W S OF 15N MOVING W 10 TO 15 KT.
THIS WAVE HAS BEEN REPOSITIONED SLIGHTLY TO THE E OF THE
PREVIOUS POSITION DUE TO THIS MORNINGS VISIBLE SATELLITE
IMAGERY...AND THE CONVECTIVE PATTERN IN THE SW CARIBBEAN.
SCATTERED MODERATE CONVECTION SEEN FROM 9N-14N BETWEEN 77W AND
84W. THIS ACTIVITY IS BEGINNING TO SPREAD INTO COASTAL CENTRAL
AMERICA.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 13N23W 16N36W 11N44W 10N60W.
SCATTERED STRONG CONVECTION IS WITHIN 150 NM N OF THE AXIS E OF
18W TO INLAND OVER AFRICA. OUTSIDE OF THE CONVECTION ASSOCIATED
WITH THE TROPICAL WAVES AND HELENE...CLUSTERS OF SCATTERED
MODERATE CONVECTION ARE SEEN FROM 12N-14N BETWEEN 29W-32W AND
13N-17N BETWEEN 33W-37W (JUST E OF HELENE). SCATTERED
SHOWERS/ISOLATED TSTMS APPROACHING NE S AMERICA FROM 7N-9N
BETWEEN 54W-60W.

...DISCUSSION...

GULF OF MEXICO...
BROAD DEEP LAYERED TROUGH COVERS THE E US...THE W ATLC AND ERN
GULF IS ANCHORED BY AN UPPER LOW MOVING SSW THROUGH UPSTATE NEW
YORK. UPPER DIFFLUENT AIR BETWEEN THE WRLY FLOW AROUND THE SSW
PORTION OF THIS UPPER TROUGH...AND NRLY FLOW AROUND AN UPPER
HIGH OVER CENTRAL MEXICO...IS HELPING TO SUPPORT THE SCATTERED
SHOWERS AND TSTMS IN THE MIDDLE GULF FROM 24N-28N BETWEEN
90W=94W. LOW CLOUD MOTIONS AND SFC OBSERVATIONS IN THE ERN GULF
SUGGESTS A WEAK SFC HIGH MAY HAVE FORMED NEAR 25N86W. E OF THIS
AREA LIES THE COLD FRONT BOUNDARY WE HAVE BEEN TRACKING THAT
EXTENDS THROUGH THE SW NORTH ATLC AND OVER SRN FLORIDA.

CARIBBEAN SEA...
THE MAJORITY OF THE WEATHER IN THE CARIBBEAN THIS AFTERNOON IS
BEING PRODUCED BY THE TROPICAL WAVES MOVING THROUGH AS DESCRIBED
ABOVE. THE W/NW CARIBBEAN IS DOMINATED BY NE UPPER FLOW...WITH
AN UPPER TROUGH AXIS EXTENDING THROUGH CENTRAL AMERICA AND ERN
CUBA ALONG 15N84W 20N77W. A SMALL MID TO UPPER LEVEL ANTICYCLONE
IS DRIFTING N THROUGH THE CENTRAL CARIBBEAN...CENTERED NEAR
15N74W. THE FAR ERN CARIBBEAN HAS VERY DRY MID TO UPPER LEVEL
AIR BEING ADVECTED INTO THE REGION FROM THE E...AROUND THE ERLY
FLOW SSW OF THE UPPER ANTICYCLONE IN THE TROPICAL ATLC NEAR
22N59W. 10 TO 20 KT TRADES DOMINATE MUCH THE THE AREA...EXCEPT
SLIGHTLY STRONGER JUST N OF THE COLOMBIAN/VENEZUELAN COASTS AND
SLIGHTLY WEAKER FAR NW PORTION.

ATLANTIC OCEAN...
BROAD DEEP LAYERED TROUGH THAT COVERS THE E US AND ERN GULF HAS
AN ASSOCIATED FRONTAL BOUNDARY THAT EXTENDS NE FROM SOUTH
CENTRAL FLORIDA AND INTO THE TROPICAL SW NORTH ATLC ALONG 26N81W
31N74W. PREFRONTAL LIFT IS GENERATING NUMEROUS SHOWERS AND TSTMS
MAINLY WITHIN 100NM SE OF THE ANALYZED COLD FRONT BOUNDARY. A
NARROW MID TO UPPER LEVEL RIDGE AXIS LIES JUST E OF THIS FRONTAL
SYSTEM...ALONG 24N79W 27N73W 31N65W. THERE ALSO APPEARS TO BE
SOME LOW LEVEL CONFLUENCE IN THIS REGION ASSOCIATED WITH THE
PREFRONTAL SW FLOW MEETING THE SE/S FLOW AROUND THE 1016 ISOBAR
THAT CURVES ANTICYCLONICALLY FROM THE 1027MB HIGH S OF THE
AZORES. THIS IS HELPING TO PRODUCE THE SCATTERED SHOWERS AND
TSTMS BETWEEN THE SE BAHAMAS AND 30N68W. A SMALL UPPER LOW IS
SEEN NEAR 30N60W. S OF THIS LIES A WELL DEFINED MID TO UPPER
HIGH NEAR 21N59W. A BROAD UPPER RIDGE EXTENDS W FROM THE AFRICAN
COAST TO NEAR 35W MAINLY N OF 20N...WITH AN EMBEDDED UPPER LOW
SEEN NEAR 20N24W.  THE CENTRAL AND ERN ATLC SURFACE PATTERN IS
DOMINATED BY HURRICANE GORDON NEAR 31N53W...T.S. HELENE NEAR
16N41W...THE TROPICAL WAVE MOVING OFF THE AFRICAN COAST...AND
THE 1027MB SURFACE HIGH S OF THE AZORES NEAR 34N25W.


$$
WILLIS






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