[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171800
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON SEP 17 2007

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1730 UTC.

...TROPICAL WAVES...

TROPICAL WAVE WAS ADDED TO THE 17/1200 UTC MAP ALONG 18W/19W S
OF 16N...ESTIMATED TO BE MOVING W NEAR 10-15 KT. AS NOTED IN THE
PREVIOUS DISCUSSION...THE WAVE PASSAGE WAS EVIDENT IN THE RECENT
DAKAR RAOB DATA. THE FEATURE ALSO SHOWS UP WELL AS A LOW
AMPLITUDE MOISTURE SURGE ON THE UW-CIMSS TPW PRODUCT. THE
ASSOCIATED...DISORGANIZED SCATTERED MODERATE CONVECTION IS
PUSHING AWAY FROM THE AFRICAN COAST FROM 5N-12N BETWEEN 17W-22W.

TROPICAL WAVE IS GENERALLY ALONG 43W S OF 19N MOVING W 10-15 KT.
A WEAK 1012 MB LOW IS ALONG THE WAVE AXIS NEAR 12.5N...BUT IS
RATHER ELONGATED AS SHOWN BY A QUIKSCAT PASS EARLIER THIS
MORNING...WITH WINDS GENERALLY 5-15 KT IN THE IMMEDIATE
VICINITY. THE WAVE IS ASSOCIATED WITH A LARGE BUT DISORGANIZED
AREA OF SHOWERS AND THUNDERSTORMS....AND ANY DEVELOPMENT OF THIS
SYSTEM IS EXPECTED TO BE SLOW TO OCCUR. SCATTERED MODERATE IS
WITHIN 210 NM E OF THE AXIS FROM 8N-15N...WITH ISOLATED MODERATE
WITHIN 210 NM W OF THE AXIS FROM 11N-16N.

TROPICAL WAVE IS IN THE CENTRAL CARIBBEAN ALONG 75W S OF 20N
MOVING W 10-15 KT. THE SHOWER/TSTM ACTIVITY ASSOCIATED WITH THIS
WAVE HAVE DIMINISHED QUITE A BIT OVER THE LAST SEVERAL
HOURS...AND UPPER-LEVEL WINDS ARE NOT FAVORABLE FOR DEVELOPMENT
IN THIS AREA OVER THE NEXT COUPLE OF DAYS. SHOWERS/TSTMS ARE
MOSTLY ISOLATED IN NATURE NOW WITHIN 180 NM EITHER SIDE OF THE
AXIS. THERE APPEARS TO BE MORE LOW LEVEL CYCLONIC TURNING NEAR
THE SE BAHAMAS...WHICH MAY BE THE NRN PORTION OF THIS WAVE THAT
HAS FRACTURED. WILL LIKELY INTRODUCE THIS AS A TROUGH ON THE
1800 UTC MAP.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 13N16W 7N28W 13N41W 10N50W 7N60W.
OUTSIDE OF THE CONVECTION ASSOCIATED WITH THE TROPICAL
WAVES...SCATTERED CLUSTERS OF MODERATE CONVECTION ARE S OF THE
AXIS FROM 3N-7N BETWEEN 22W-33W. SCATTERED MODERATE ALSO WITHIN
90 NM EITHER SIDE OF THE AXIS BETWEEN 46W-53W.

DISCUSSION...

GULF OF MEXICO...
A DISSIPATING FRONTAL BOUNDARY IS AFFECTING THE GULF THIS
AFTERNOON...WITH THE WANING BOUNDARY EXTENDING FROM THE W COAST
OF FLORIDA NEAR 27N82W TO JUST OFFSHORE S TEXAS NEAR 26N97W.
ISOLATED SHOWERS/TSTMS ARE GENERALLY WITHIN 90 NM OF THE
BOUNDARY...BUT HAVE DIMINISHED SOME SINCE EARLY THIS MORNING.
ANOTHER CLUSTER OF MODERATE CONVECTION IS OVER THE NE GULF NEAR
28N96W WHICH ALSO APPEARS TO BE SOMEWHAT RELATED TO THE DYING
FRONT...BUT CLOSER TO WHERE THE LOW LEVEL MOISTURE GRADIENT
EXISTS INSTEAD OF THE WIND SHIFT. THIS ACTIVITY IS ALSO
OCCURRING NEAR THE BASE OF THE DOMINATING MID TO UPPER TROUGH
OVER THE EAST COAST.  THE ONLY OTHER ACTIVITY NOTED ARE A FEW
TSTMS IN THE BAY OF CAMPECHE S OF 20N BETWEEN 93W-96W...WHICH
ARE ASSOCIATED WITH LIFT AHEAD OF THE UPPER LOW OVER MEXICO NEAR
21N98W. THE REMAINDER OF THE UPPER PATTERN IS DOMINATED BY
RIDGING...EXTENDING N/NW FROM AN UPPER HIGH NEAR 22N89W THROUGH
ERN TEXAS. SFC RIDGING BUILDING BEHIND THE DYING FRONT WILL TAKE
OVER MUCH OF THE GULF N OF 25N THROUGH TUE...WITH WEAK TROUGHING
TO THE S. SOME OF THE GLOBAL MODELS ARE SUGGESTING A SFC LOW
WILL DEVELOP IN THE ERN GULF LATER IN THE WEEK...BUT THE EXACT
TIMING...LOCATION...AND INTENSITY OF THIS FEATURE ARE HIGHLY
UNCERTAIN AT THIS POINT.

CARIBBEAN SEA...
A WEAK SFC TROUGH IS OVER THE NW CARIBBEAN EXTENDING FROM THE
COAST OF WRN CUBA NEAR 23N82W TO 16N83W. A BROAD REGION OF LOW
LEVEL TURNING REMAINS EVIDENT NEAR THIS TROUGH...WITH WINDS
REMAINING MOSTLY BELOW 15 KT. THE TROUGHING IS PRODUCING A FEW
ISOLATED TSTMS N OF 15N W OF 78W. THE OTHER SFC FEATURE
AFFECTING THE BASIN IS THE TROPICAL WAVE IN THE CENTRAL PORTION
AS DESCRIBED ABOVE. THE REMNANT LOW ASSOCIATED WITH TROPICAL
DEPRESSION INGRID IS LOCATED JUST EAST OF THE NORTHERNMOST
LEEWARD ISLANDS.  REDEVELOPMENT OF THIS SYSTEM IS NOT EXPECTED
DURING THE NEXT COUPLE OF DAYS AS IT MOVES SLOWLY W TO WNW. A
CLUSTER OF MODERATE CONVECTION IS JUST OFFSHORE NICARAGUA FROM
10N-13N BETWEEN 82W-84W...THAT IS OCCURRING AT THE BASE OF THE
UPPER TROUGHING EXTENDING SW FROM WRN HAITI TO 10N84W. A SIMILAR
CLUSTER OF MODERATE CONVECTION IS JUST N OF THE
COLOMBIA/VENEZUELA BORDER FROM 12N-15N BETWEEN 70W-73W...WHICH
SEEMS ASSOCIATED WITH UPPER DIVERGENCE BETWEEN THE
AFOREMENTIONED UPPER TROUGH AND UPPER RIDGING OVER THE ERN
CARIBBEAN. LIGHT TO MODERATE TRADES ARE IN PLACE AND EXPECTED TO
PERSIST THROUGH MIDWEEK.

ATLANTIC OCEAN...
THE DOMINATING FEATURE OF THE WRN ATLC IS THE STATIONARY FRONT
THAT ENTERS THE AREA NEAR 32N72W AND CONTINUES TO CENTRAL
FLORIDA NEAR 28N81W. THIS...IN ADDITION TO ITS SUPPORTING MID TO
UPPER TROUGH OVER THE EAST COAST...IS PRODUCING NUMEROUS SHOWERS
AND TSTMS N OF 28N W OF 72W TO THE COAST OF FLORIDA. MODERATE TO
FRESH NE WINDS ARE COMMON BEHIND THE FRONT WHICH HAVE USHERED IN
SOME PLEASANT...FALL-LIKE WEATHER INTO THE SOUTHEAST U.S.
SCATTERED SHOWERS AND TSTMS ARE OVER THE BAHAMAS AND ADJACENT
WATERS S OF 26N BETWEEN 73W-79W. SOME LOW LEVEL TURNING IS NOTED
IN THIS REGION WHICH WILL LIKELY BE ADDED AS A TROUGH ON THE
1800 UTC MAP. SCATTERED SHOWERS AND TSTMS ARE OVER THE CENTRAL
ATLC WATERS FROM 23N-28N BETWEEN 51W-60W...PRIMARILY TIED TO THE
UPPER LOW NEAR 26N61W. THERE IS ALSO A SFC TROUGH IN THE REGION
ALONG 29N54W 27N62W 24N64W. A FEW SMALL CLUSTERS OF MODERATE
CONVECTION ARE ALSO E OF THE REMNANT LOW ASSOCIATED WITH FORMER
TROPICAL DEPRESSION INGRID...FROM 15N-21N BETWEEN 56W-60W. CLOUD
TOPS OVER THE ACTIVITY CONTINUE TO BE STRETCHED TO THE E WITH
PERSISTENT WLY SHEAR OVER THE AREA. ANOTHER WEAK SFC TROUGH
ENTERS THE AREA NEAR 32N36W AND CONTINUES S/SW THROUGH 28N36W
26N42W. ISOLATED SHOWER ACTIVITY IS WITHIN 60NM MAINLY E OF THIS
BOUNDARY. TYPICAL SFC RIDGING IS OVER THE REMAINDER OF THE E
ATLC PRODUCING MODERATE NE TRADES E OF 30W...STRONGEST ALONG THE
NW COAST OF AFRICA. UPPER RIDGING IS OVER THE TROPICAL ATLC WITH
UPPER HIGH CENTERS ESTIMATED TO BE NEAR 13N45W AND 17N25W.
EXTENSIVE WLY FLOW ALOFT IS NORTH OF THESE HIGHS E OF 58W.

$$
WILLIS


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