[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 240459
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT SUN SEP 24 2006

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0315 UTC.

...SPECIAL FEATURES...
HURRICANE HELENE IS CENTERED NEAR 39.1N 41.7W OR ABOUT 691 NM
WEST OF THE AZORES AT 24/0300 UTC MOVING EAST-NORTHEAST AT 20
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 973 MB. MAXIMUM
SUSTAINED WIND SPEED IS 75 KT WITH GUSTS TO 90 KT. SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/
WTNT23 KNHC FOR MORE DETAILS. HELENE RETAINS TROPICAL
CHARACTERISTICS BUT IS IS EXPECTED TO BECOME EXTRATROPICAL OVER
THE NEXT 12 TO 24 HOURS. SCATTERED MODERATE CONVECTION IS WITHIN
250 NM OF THE CENTER IN THE NW QUADRANT. DENSE OVERCAST CLOUDS
WITH SHOWERS/THUNDERSTORMS IS FROM 37N-45N BETWEEN 37W-47W.

...TROPICAL WAVES...
A 1009 MB LOW IS CENTERED NEAR 19N41W MOVING N 10 KT. LOW WAS
PREVIOUSLY ASSOCIATED WITH THE WAVE THAT HAS MOVED FURTHER W AND
APPEARS TO BE MOVING N IN RESPONSE TO AN UPPER RIDGE. CLUSTERS
OF SCATTERED MODERATE/STRONG CONVECTION COVER THE AREA FROM
18N-23N BETWEEN 36W-44W.

TROPICAL WAVE IS ALONG 44W/45W S OF 19N MOVING W 10 KT. THIS
WAVE HAS WEAKENED CONSIDERABLY SINCE THE ASSOCIATED LOW BROKE
AWAY ON SAT AFTERNOON. WAVE IS EMBEDDED WITHIN DRY AIR AND HAS
NO ASSOCIATED SHOWERS/CONVECTION.

TROPICAL WAVE IS OVER THE LESSER ANTILLES ALONG 61W/62W S OF 20N
MOVING W 10-15 KT. BROAD INVERTED-V SIGNATURE CURVATURE
ASSOCIATED WITH THIS WAVE. SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS ARE FROM 12N-18N BETWEEN 57W-63W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 7N29W 13N38W BECOMING
DISTORTED BY THE TROPICAL LOW/WAVE THEN ALONG 10N49W 13N60W
9N62W ACROSS N PORTION OF SOUTH AMERICA AND PANAMA INTO THE E
PACIFIC REGION NEAR 9N80W. APART FROM THE CONVECTION ASSOCIATED
WITH THE TROPICAL LOW/WAVE...SCATTERED STRONG CONVECTION IS
WITHIN 150 NM N OF THE ITCZ AXIS FROM 21W-24W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 250 NM S OF THE
ITCZ AXIS FROM 19W-27W WITH CLUSTERS OF SIMILAR CONVECTION FROM
11N-17N BETWEEN 37W-43W.

...DISCUSSION...
GULF OF MEXICO...
BROAD UPPER TROUGH EXTENDS FROM AN UPPER LOW OVER THE GREAT
LAKES INTO TEXAS MOVING INTO THE MISSISSIPPI VALLEY WITH THE
ASSOCIATED STRONG COLD FRONT STILL INLAND OVER THE TEXAS COAST.
A SQUALL LINE IS ALONG THE TEXAS COAST FROM PORT ARTHUR TO JUST
S OF GALVESTON AND WILL BE ENTERING THE NW GULF SHORTLY. AN
UPPER HIGH IS CENTERED OVER NE MEXICO NEAR 23N99W WITH A BROAD
RIDGE COVERING THE W GULF W OF 90W. ANOTHER UPPER HIGH IS
ANCHORED IN THE W ATLC EXTENDING A RIDGE OVER THE E GULF E OF
85W. THE UPPER LOW IS SQUEEZED BETWEEN THESE RIDGES AND CENTERED
IN THE SE GULF N OF THE YUCATAN PENINSULA NEAR 23N88W GENERATING
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 24N FROM 83W-87W.
MODERATE/STRONG RETURN SURFACE FLOW REMAINS OVER MUCH OF THE
GULF.

CARIBBEAN SEA...
THE UPPER LOW CENTERED IN THE SE GULF COVERS A SMALL PORTION OF
NW CARIBBEAN N OF 19N W OF 85W WITH SCATTERED SHOWERS N OF 19N W
OF 83W. BROAD UPPER RIDGE OVER THE W ATLC IS GENERATING
SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS N OF 17N
FROM 71W-83W AND GIVING THE REMAINDER OF THE CARIBBEAN NE UPPER
FLOW WITH MOSTLY DRY AIR. OTHER THAN THE SHOWER ACTIVITY
ASSOCIATED WITH THE TROPICAL WAVE OVER THE LESSER ANTILLES THE
REMAINDER OF THE CARIBBEAN REMAINS CLEAR TONIGHT.

ATLANTIC OCEAN...
BROAD UPPER RIDGE COVERS THE W ATLC ANCHORED BY AN UPPER HIGH
NEAR 29N74W AND COVERS THE AREA W OF 62W AND GIVING THE
CARIBBEAN NE UPPER FLOW. WEAK UPPER TROUGH EXTENDS FROM 25N45W
SW TO JUST E OF THE LEEWARD ISLANDS NEAR 18N59W AND IS ENHANCING
THE SHOWER ACTIVITY ASSOCIATED WITH THE TROPICAL WAVE OVER THE
LESSER ANTILLES. A DEEP LAYERED TROUGH IS PUSHING SE OVER THE
CANARY ISLANDS WITH THE ASSOCIATED STATIONARY FRONT N OF THE
REGION. BROAD UPPER HIGH ANCHORED NW OF THE CAPE VERDE ISLANDS
NEAR 18N27W COVERS THE REMAINDER OF THE E ATLC. AT THE
SURFACE...A SURFACE TROUGH IS IN THE CENTRAL ATLC FROM BEYOND
32N41W SW TO 25N58W IN THE WAKE OF HURRICANE HELENE SPLITTING
THE SUBTROPICAL RIDGE THAT DOMINATES THE MUCH OF THE ATLC. W
ATLC SURFACE RIDGE EXTENDS FROM A 1023 MB HIGH WELL N OF THE
REGION THROUGH 32N68W ACROSS TO OVER FLORIDA NEAR 28N84W. THE E
ATLC RIDGE COVERS THE REGION N OF 18N FROM 20W-37W ANCHORED BY A
1020 MB HIGH NEAR 32N30W.

$$
WALLACE




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