[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 161800
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT SEP 16 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...
HURRICANE GORDON IS CENTERED NEAR 31.3N 53.7W OR ABOUT 655
MILES...1055 KM...EAST OF BERMUDA AT 16/1500 UTC AND
IS NEAR STATIONARY. ESTIMATED MINIMUM CENTRAL PRESSURE IS 987
MB. MAXIMUM SUSTAINED WIND SPEED IS 65 KT WITH GUSTS TO 80 KT.
SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. GORDON REMAINS IN A WEAK
STEERING ENVIRONMENT AND HAS CHANGED LITTLE TODAY. THE CYCLONE
IS FAIRLY SYMMETRIC WITH A RAGGED EYE ABOUT 30-40 NM IN
DIAMETER. CONVECTION IS NOT VERY DEEP AROUND THE SYSTEM...THE
COLDEST OF THE CLOUD TOPS ARE NEAR -70 C IN A SMALL AREA IN THE
EASTERN EYEWALL. GORDON HAS BEEN A COMPACT SYSTEM THROUGHOUT ITS
LIFE WITH ITS RAIN FIELD COVERING AN AREA OF LESS THAN 300 NM
ACROSS FROM 30N-33N BETWEEN 52W-56W .

HELENE HAS BEEN UPGRADED TO A HURRICANE. HELENE IS CENTERED NEAR
18.8N 45.6W OR ABOUT 1145 MILES...1845 KM...EAST OF THE NORTHERN
LEEWARD ISLANDS 16/1500 MOVING WEST-NORTHWEST AT 12 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 987 MB. MAXIMUM SUSTAINED
WIND SPEED IS 65 KT WITH GUSTS TO 80 KT. SEE THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
FOR MORE DETAILS. UNLIKE GORDON...HELENE IS A LARGE SYSTEM WITH
SCATTERED MODERATE CONVECTION COVERING AN AREA FROM 16N-24N
BETWEEN 42W-49W. THE STRONGEST CONVECTION EXISTS TO THE N AND W
OF THE CENTER. LARGE BANDING FEATURES ARE IMPROVING WITH A
POSSIBLE RAGGED EYE FEATURE ATTEMPTING TO FORM.

...TROPICAL WAVES...
A 1011 MB LOW PRES AREA IS IN THE E ATLC CENTERED NEAR
16N21W...ABOUT 150 NM E OF THE CAPE VERDE ISLANDS. THIS LOW HAS
BEEN RELOCATED TO THE E OF THE PREVIOUS POSITION. THE LOW LEVEL
CENTER IS FAIRLY EASY TO SEE ON VISIBLE IMAGES AS IT IS
PARTIALLY EXPOSED AND LIES NEAR THE SOUTHERN EDGE OF THE
CONVECTION. BASED UPON THIS STRUCTURE...THIS LOW PRES AREA IS
FEELING EFFECTS OF S-SW VERTICAL WIND SHEAR. WEAKENING SCATTERED
MODERATE IS FROM 17N-22N BETWEEN 19W-23W. DEVELOPMENT...IF
ANY...WOULD BE SLOW TO OCCUR AS IT TRACKS NW NEAR 10 KT.

TROPICAL WAVE IS ALONG 78W S OF 17N MOVING W NEAR 15 KT. SOME
LOW-MID LEVEL CYCLONIC TURNING IS NOTED ON VIS IMAGES ABOUT THE
AXIS. A FAIRLY LARGE AREA OF DEEP CONVECTION IS IN THE SW
CARIBBEAN AHEAD OF THE ANALYZED AXIS FROM 9N-18N BETWEEN
79W-86W...LIKELY ENHANCED BY UPPER LEVEL DIFFLUENT FLOW.

TROPICAL WAVE IS ALONG 86W S OF 16N MOVING W NEAR 15 KT. THE
WAVE IS ENHANCING THE ITCZ TO LIFT NWD. SCATTERED MODERATE
CONVECTION LIES MAINLY TO THE E OF THE WAVE ENHANCED BY THE WAVE
JUST TO ITS E.


WELL-DEFINED LOW/MID LEVEL INVERTED-V SATELLITE SIGNATURE IS
OBSERVED IN THE E PACIFIC REGION AS THE N PORTION IS INLAND OVER
CENTRAL AMERICA. WAVE IS BENEATH THE WESTERN EDGE OF AN UPPER
RIDGE WITH SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
13N-16N BETWEEN 82W-84W.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 6N10W 10N32W 15N40W 12N43W TO THE
COAST OF SOUTH AMERICA NEAR 9N61W. BESIDES FOR THE CONVECTION
ASSOCIATED WITH HELENE AND THE E ATLC LOW...THE ONLY OTHER AREA
IS MOVING OFF THE W COAST OF AFRICA WHERE THERE IS SCATTERED
MODERATE E OF 15W FROM 7N-12N.

...DISCUSSION...

GULF OF MEXICO...
FAIRLY QUIET CONDITIONS EXIST IN THE GULF THIS AFTERNOON. AN
UPPER LEVEL TROUGH STRETCHES FROM THE NE U.S. OFF THE U.S. EAST
COAST AND ACROSS S FLORIDA. MID TO UPPER RIDGING EXTENDS FROM
MEXICO NORTHEASTWARD TO THE SOUTH CENTRAL U.S. UPPER DIFFLUENCE
BETWEEN THESE FEATURES IS TRIGGERING SCATTERED SHOWERS AND
ISOLATED TSTMS IN THE CENTRAL GULF FROM 25N-28N BETWEEN
88W-90W...MOVING SW ON THE E PERIPHERY OF THE MID LEVEL RIDGE.
OTHERWISE...FAIR WEATHER IS THE RULE MAINLY DUE TO VERY DRY
STABLE UPPER LEVEL AIR IN PLACE. THE DRIEST AIR IS ACROSS THE NE
GULF. AT THE SFC...HIGH PRES CENTERED ACROSS THE GREAT LAKES IS
BUILDING INTO THE AREA. LIGHT E-SE WINDS COVER THE E GULF...WITH
STRONGER 15 KT SLY RETURN FLOW IN THE W GULF. LITTLE SIGNIFICANT
PATTERN CHANGE IS EXPECTED TOMORROW. A COLD FRONT WILL LIKELY
ENTER THE NORTHERN GULF LATE MON BRINGING THE NEXT CHANCE OF
ORGANIZED RAINFALL.

CARIBBEAN SEA...
THE MOST ACTIVE WEATHER IN THE REGION IS IN THE SW CARIBBEAN
WHERE SCATTERED MODERATE CONVECTION EXISTS FROM 9N-13N BETWEEN
78W-83W. OVER THE LAST FEW HOURS...A LINE OF SIMILAR CONVECTION
HAS BECOME MORE ACTIVE FROM 13N-18N BETWEEN 82W-85W. THIS
ACTIVITY IS LIKELY ENHANCED BY UPPER LEVEL DIFFLUENCE ON THE S
SIDE OF A SMALL UPPER HIGH AND SFC CONVERGENCE IN THE VICINITY
OF A COUPLE TROPICAL WAVES. THIS ENTIRE CONVECTIVE MASS IS
MOVING WESTWARD TOWARDS CENTRAL AMERICA. A WEAK UPPER LOW IN THE
SE BAHAMAS IS ALSO HELPING TO PRODUCE A FAIR AMOUNT OF MID-HIGH
LEVEL CLOUDINESS AND SCATTERED SHOWERS IN THE NW CARIBBEAN...BUT
A LIMITED AMOUNT OF DEEP MOISTURE. A MID-LEVEL RIDGE IN THE
CENTRAL ATLC IS ADVECTING DRY AIR INTO THE CARIBBEAN E OF 73W.
THIS DRY AIR WILL CONTINUE TO PRESS WESTWARD ACROSS THE
CARIBBEAN OVER THE NEXT COUPLE OF DAYS AND WILL LIKELY LIMIT
WIDESPREAD DEVELOPMENT OF DEEP CONVECTION AS IT DOES SO. TRADE
WINDS ARE GENERALLY IN THE 15-25 KT RANGE AND THESE WINDS ARE
EXPECTED TO REMAIN THAT WAY THRU TOMORROW.

ATLANTIC OCEAN...
A DEEP LAYER TROUGH HAS MOVED OFF THE E COAST OF THE U.S WITH
THE UPPER AXIS EXTENDING INTO THE BAHAMAS AND S FLORIDA. VERY
DRY AIR LIES ALONG AND TO THE W OF THE AXIS W OF 76N N OF 27N.
AN ASSOCIATED COLD FRONT EXTENDS FROM A 1011 MB LOW NEAR 35N72W
ALONG 32N70W 28N75W THEN AS A DISSIPATING FRONT TO 27N79W.  A
PRE-FRONTAL SFC TROUGH ENTERS THE AREA NEAR 32N65W AND CONTINUES
SW ALONG 27N71W TO THE W BAHAMAS. SCATTERED SHOWERS AND TSTMS
ARE WITHIN 300 NM AHEAD OF THE SFC FRONT. A WEAK MID-UPPER LEVEL
RIDGE COVERS THE CENTRAL ATLC WITH A HIGH CENTER NEAR
22N56W. DRY UPPER LEVEL AIR COVERS THE MAJORITY OF THE AREA
BETWEEN 50W-70W. A WEAK 1019 MB HIGH IS LOCATED NEAR 24N61W
HELPING TO KEEP THE WEATHER CONDITIONS TRANQUIL IN THIS ZONE.
GORDON REMAINS N OF THIS UPPER RIDGE IN VERY WEAK STEERING
CURRENTS KEEPING THE STORM NEARLY STATIONARY. RECENTLY UPGRADED
HURRICANE HELENE IS MOVING TOWARDS THE NW INTO A WEAKNESS IN THE
RIDGE PARTIALLY INDUCED BY HURRICANE GORDON. AN UPPER TROUGH
LIES TO THE E OF THE HURRICANES N OF 22N FROM 25W-41W. AN UPPER
LEVEL RIDGE IS INLAND OVER AFRICA. ALL OF THE SIGNIFICANT
CONVECTION IN THE CENTRAL AND E ATLC IS ASSOCIATED WITH
GORDON...HELENE AND THE E ATLC LOW PRES SYSTEM DISCUSSED ABOVE.

$$
CANGIALOSI


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