[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 171053
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SUN SEP 17 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1045 UTC.

...SPECIAL FEATURES...
HURRICANE GORDON WAS CENTERED NEAR 32.6N 53.3W OR ABOUT 580 NM
EAST OF BERMUDA AT 17/0900 UTC MOVING NORTH NEAR 5 KT. A TURN
TOWARD THE NORTHEAST WITH A GRADUAL INCREASE IN FORWARD SPEED IS
EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 987 MB. MAXIMUM SUSTAINED WINDS ARE 65 KT WITH GUSTS
TO 80 KT. SOME SLOW WEAKENING IS FORECAST DURING THE NEXT 24
HOURS. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. SCATTERED
MODERATE CONVECTION ASSOCIATED WITH GORDON LIES FROM 31N-35N
BETWEEN 51W-55W.

HURRICANE HELENE WAS CENTERED NEAR 20.0N 48.2W OR ABOUT 850 NM
EAST OF THE NORTHERN LEEWARD ISLANDS AT 17/0900 UTC MOVING
NORTHWEST AT 8 KT. A MOTION BETWEEN WEST-NORTHWEST AND
NORTHWEST IS EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 979 MB. MAXIMUM SUSTAINED WINDS ARE
75 KT WITH GUSTS TO 90 KT. SOME STRENGTHENING IS FORECAST DURING
THE NEXT 24 HOURS. SEE THE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS.
NUMEROUS MODERATE/ISOLATED STRONG CONVECTION ASSOCIATED WITH
HELENE LIES FROM 18N-24N BETWEEN 45W-50W.

...TROPICAL WAVES...
A BROAD 1012MB LOW NEAR 17N22W...MOVING WNW 5-10 KT...IS NEAR
THE EASTERN CAPE VERDE ISLANDS BUT DEEP CONVECTION REMAINS
MINIMAL OVERALL. THERE IS A SMALL CLUSTER OF SCATTERED
MODERATE/ISOLATED STRONG CONVECTION N OF THE LOW FROM 19N-20N
BETWEEN 21W-23W...WHICH MAY BE GETTING MORE SUPPORT FROM THE
UPPER DIFFLUENT AIR BETWEEN THE UPPER TROUGH TO THE WNW AND THE
UPPER HIGH OVER WRN AFRICA. DEVELOPMENT OF THIS SYSTEM IS NOT
EXPECTED DUE TO UNFAVORABLE UPPER-LEVEL WINDS AND COOL OCEAN
TEMPERATURES.

A WESTERN CARIBBEAN TROPICAL WAVE IS ALONG 82W S OF 20N MOVING W
10 TO 15 KT. THERE IS STILL A WEAK INVERTED V PATTERN SEEN ON
SATELLITE IMAGERY BUT THE SIGNAL IS NOT AS CLEAR CUT AS IT HAS
BEEN. THE DEEP CONVECTION ASSOCIATED WITH THIS WAVE HAS
DIMINISHED IN BOTH COVERAGE AND INTENSITY OVER THE LAST
12HRS...WITH ISOLATED SHOWERS AND TSTMS NOW SEEN FROM 12N-22N
BETWEEN 77W-86W.

TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 90W/91W S OF 18N
MOVING W 10 TO 15 KT. THE ASSOCIATED DEEP CONVECTION IS NOW
MOVING INTO THE EPAC WATERS FROM 11N-16N BETWEEN 89W-94W. THERE
ALSO APPEARS TO BE SOME SUBTLE CYCLONIC TURNING OF THE LOW TO
MID CLOUD FIELD IN THIS REGION.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N13W 10N37W 16N43W 16N51W TO INLAND
OVER SOUTH AMERICA NEAR 9N61W...EMERGING INTO THE SRN CARIBBEAN
AND TO THE COAST OF PANAMA NEAR 9N78W. THE CLUSTER OF SCATTERED
MODERATE CONVECTION THAT MOVED OFF THE COAST OF SIERRA LEONE
LAST NIGHT IS NOW FROM 6N-9N BETWEEN 14W-17W. ISOLATED
SHOWERS/TSTMS ARE WITHIN 100NM OF EITHER SIDE OF THE AXIS
BETWEEN 25W-42W. PATCHES OF SCATTERED MODERATE/ISOLATED STRONG
CONVECTION ALSO SEEN OVER NW COLOMBIA AND THE SW CARIBBEAN FROM
7N-12N BETWEEN 74W-80W.

...DISCUSSION...

GULF OF MEXICO...
LITTLE SIGNIFICANT WEATHER IS AFFECTING THE GULF THIS
MORNING...WITH ABUNDANT DRY MID TO UPPER LEVEL AIR HOVERING OVER
THE AREA. THERE ARE A FEW ISOLATED SHOWERS IN THE MIDDLE GULF
WATERS FROM 22N-26N BETWEEN 87W-94W...ASSOCIATED WITH UPPER
DIFFLUENT AIR BETWEEN THE FLOW AROUND AN UPPER ANTICYCLONE OVER
MEXICO AND THE TROUGHING OFF THE U.S. EAST COAST. THESE SMALL
CELLS ARE BARELY ABLE TO SUSTAIN THEMSELVES IN THE MIDST OF THE
DRY AIR PRESENT. FAIRLY LIGHT 5-15 KT ANTICYCLONIC SE/S FLOW
DOMINATES AT THE SURFACE TONIGHT. THE EXCEPTION IS 15-20KT SE/S
FLOW IN THE W/NW PORTION WHERE A SLIGHTLY STRONGER GRADIENT IS
IN TACT AS THE WRN PORTION OF HIGH PRESSURE INTERACTS WITH LOWER
PRESSURE OVER MEXICO...AND A FRONTAL SYSTEM PUSHING INTO NW
TEXAS.

CARIBBEAN SEA...
A TROPICAL WAVE IS TRAVERSING THE WRN CARIBBEAN SEA PRODUCING
CONVECTION W OF 78W AS DESCRIBED ABOVE. MUCH OF THE CARIBBEAN E
OF 78W IS DOMINATED BY DRY MID TO UPPER LEVEL AIR AND FAIR
WEATHER. THE UW-CIMMS SAHARAN AIR LAYER ANALYSIS ALSO SUGGESTS
THIS AREA IS UNDER THE INFLUENCE OF DENSE SAHARAN DUST. A MID TO
UPPER LEVEL HIGH IS OVER THE NW CARIBBEAN...WITH AN ESTIMATED
CENTER NEAR 17N83W. THERE IS A MID TO UPPER LEVEL TROUGH AXIS
THAT EXTENDS NORTH FROM VENEZUELA AND INTO THE CARIBBEAN MORE OR
LESS ALONG 68W TO NEAR THE MONA PASSAGE...BUT DRY AIR IS
INHIBITING CONVECTION. AT THE SURFACE...10-20KT TRADES DOMINATE
EXCEPT SLIGHTLY STRONGER N OF THE COLOMBIAN COAST.

ATLANTIC OCEAN...
PRONOUNCED DEEP LAYER TROUGHING OFF THE US EAST COAST IS
ANCHORED BY AN UPPER LOW ABOUT 150NM E OF RODANTHE NORTH
CAROLINA. ASSOCIATED SLOW MOVING...NOW DYING COLD FRONT IS OVER
THE W ATLC ALONG 32N68W 25N80W. THE MOST SIGNIFICANT CONVECTION
ASSOCIATED WITH THIS OLD FRONTAL BOUNDARY IS NOW MOVING THROUGH
THE SRN BAHAMAS FROM 23N-25N BETWEEN 76W-78W...ELSEWHERE
ISOLATED SHOWERS/TSTMS ARE WITHIN 75NM OF THE FRONTAL BOUNDARY.
A MID TO UPPER LEVEL HIGH IS NNE OF THE LEEWARD ISLANDS NEAR
21N62W. OUTFLOW IS SEEN IN SATELLITE IMAGERY OVER THE CENTRAL
ATLC HURRICANES GORDON AND HELENE...WITH GOES HIGH DENSITY WINDS
ALSO DEPICTING THIS WELL. A MID TO UPPER LEVEL TROUGH IS OVER
THE ERN ATLC NEAR 22N32W. UPPER DIFFLUENT AIR BETWEEN THIS
FEATURE AND THE UPPER HIGH OVER WRN AFRICA IS HELPING TO SUPPORT
THE SCATTERED SHOWERS/TSTMS FROM 19N-30N BETWEEN 16W-23W.
ELSEWHERE AT THE SURFACE...A 1016MB HIGH IS CENTERED NEAR
24N65W...WITH A 1023MB HIGH N OF THE AREA NEAR 34N38W...AND A
1022MB HIGH CENTER FURTHER E NEAR 34N17W.

$$
WILLIS


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