000
AXPZ20 KNHC 170907
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC THU SEP 17 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0845 UTC.

...SPECIAL FEATURE...

TROPICAL STORM MARTY IS LOCATED NEAR 19.7N 112.9W AT 17/03000 
UTC N-NW OR 335 DEG AT 4 KT. MAXIMUM SUSTAINED WIND SPEED IS 40 
KT WITH GUSTS TO 50 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 
1003 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO 
HEADERS MIATCMEP1/WTPZ21KNHC FOR MORE DETAILS. NUMEROUS MODERATE 
TO STRONG CONVECTION IS WITHIN 90 NM OF THE POINT 19N113.4W.
MARTY IS FORECAST TO INTENSITY SLIGHTLY TODAY BEFORE ATMOSPHERIC 
AND OCEAN CONDITIONS BECOME LESS FAVORABLE INDUCING A WEAKENING 
FRIDAY. MARTY IS EXPECTED TO BEGIN MOVING SLOWLY 
NORTH-NORTHWESTWARD SOON AS A WEAK RIDGE BUILDS TO THE EAST OF 
THE CYCLONE.   

...TROPICAL WAVE...

A TROPICAL WAVE IS ALONG 127W/128W FROM 07N TO 15N MOVING W 10 
KT. THERE IS ONLY ISOLATED CONVECTION NEAR THE WAVE AXIS. NO 
ORGANIZATION IS NOTED.

A TROPICAL WAVE IS N OF 06N ALONG 82W MOVING W 10 TO 15 KT. 
LITTLE CONVECTION IS NOTED NEAR THE WAVE AXIS.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...06N77W TO 
08N105W TO 08N140W. SCATTERED MODERATE TO STRONG CONVECTION IS 
WITHIN 60 NM OF THE POINT 07N98.5W. SCATTERED MODERATE 
CONVECTION IS WITHIN 90 NM OF THE POINT 07N139W.

...DISCUSSION...

N OF 20N...A SURFACE RIDGE...ANCHORED ON A 1021 MB HIGH PRES 
NEAR 29N135W CONTINUES TO SLIDE SOUTHWARD OVER THE N WATERS 
COVERING ROUGHLY THE AREA N OF 15N W OF 120W. THIS REGION IS 
MARKED BY MODERATE TO STRONG SUBSIDENCE WITH BROKEN 
STRATOCUMULUS CLOUDS. THIS FEATURE IS PRODUCING TRADE WINDS OF 
20 KT AND SEAS TO 9 FT BETWEEN 15N AND 20N W OF 125W. THE 
LEADING EDGE OF A COLD FRONT HAS STALLED ACROSS THE FAR NW 
CORNER OF THE AREA. A DEEP-LAYER TROUGH ACROSS THE FAR NE 
PACIFIC SUPPORTS THIS FRONTAL SYSTEM. THIS FRONT IS EXPECTED TO 
DISSIPATE E OF 130W TODAY WHILE THE W PORTION IS FORCED SW. WAVE 
HEIGHTS WILL BUILD INTO THE 8 TO 10 FT RANGE IN W-NW SWELL TODAY 
OVER THESE NW WATERS.

S OF 20N...ASIDE FROM TROPICAL STORM MARTY...THE TROPICAL 
WAVE...AND THE CONVECTION ALONG THE ITCZ...CONDITIONS ARE 
RELATIVELY QUIET OVER THE REMAINDER OF THE AREA. A DIFFLUENT 
PATTERN ALOFT ASSOCIATED WITH AN UPPER-LEVEL HIGH CENTERED OVER 
WESTERN CUBA IS HELPING TO VENTILATE AND SUSTAIN A FEW AREAS OF 
DEEP CONVECTION OVER THE EPAC WATERS AND ALONG THE ITCZ 
PARTICULARLY E OF 105W. A CLUSTER OF MODERATE TO STRONG 
CONVECTION IS N OF 15N TO THE PACIFIC COAST OF MEXICO WITH 
SCATTERED MODERATE TO STRONG CONVECTION WITHIN THE AREA FROM 15N 
TO 18N FROM 100.5W TO 104W. A LOW-LEVEL CYCLONIC CIRCULATION MAY 
BE ASSOCIATED WITH THIS ACTIVITY.

WAVE HEIGHTS ARE GENERALLY RUNNING AT 8 TO 9 FT OVER MUCH OF THE 
FORECAST AREA PRIMARILY IN NW SWELL. NEW PULSES OF S-SW LONG 
PERIOD SWELL WILL MOVE INTO THE WATERS DURING THE NEXT FEW DAYS 
AND MIX WITH W AND NW SWELL...AND RAISE WAVE HEIGHTS ABOVE 8 FT 
E OF 110W...TONIGHT THROUGH THE WEEKEND.

$$
LL/GR/SS