000
AXPZ20 KNHC 170325
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC THU SEP 17 2009

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

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...SPECIAL FEATURE...

TROPICAL STORM MARTY IS LOCATED NEAR 19.2N 112.7W AT 17/03000 
UTC N-NW OR 340 DEG AT 3 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. ALL THE DEEP 
CONVECTION ASSOCIATED WITH MARTY REMAINS OVER THE WESTERN 
SEMICIRCLE OF THE STORM...INDICATING THAT THE CYCLONE IS 
EXPERIENCING SOME SLY SHEAR. THERE IS A VERY SHORT PERIOD 
TONIGHT THROUGH THURSDAY FOR MARTY TO INTENSITY BEFORE 
ATMOSPHERIC AND OCEAN CONDITIONS BECOME LESS FAVORABLE INDUCING 
A MORE RAPID RATE OF WEAKENING. 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 126W MOVING W 10 KT. THERE IS ONLY 
ISOLATED CONVECTION WITHIN THE ITCZ ASSOCIATED WITH THIS WAVE.

A TROPICAL WAVE OVER THE CARIBBEAN SEA EXTENDS SOUTH TO 06N INTO 
THE FAR EPAC THROUGH PANAMA. ISOLATED CONVECTION IS NOTED OVER 
THE GULF OF PANAMA.  

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE 10N85W TO 
07N100W TO 10N114W TO 13N122W TO 10N140W. SCATTERED MODERATE TO 
ISOLATED STRONG CONVECTION IS WITHIN 120 NM N OF AXIS BETWEEN 
100W AND 103W. SCATTERED MODERATE CONVECTION IS SEEN FROM 05N TO 
10N W OF 137W. 

...DISCUSSION...

N OF 20N...A SURFACE RIDGE...ANCHORED ON A 1021 MB HIGH PRES 
NEAR 29N132W CONTINUES TO SLIDE SOUTHWARD OVER THE N WATERS 
COVERING ROUGHLY THE AREA N OF 15N W OF 118W. 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 THU...WHILE THE W PORTION IS FORCED SW. WAVE 
HEIGHTS WILL BUILD INTO THE 8 TO 10 FT RANGE IN W-NW SWELL 
TONIGHT AND THU 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 FROM 101W 
TO 103W. A LOW-LEVEL CYCLONIC CIRCULATION MAY BE ASSOCIATED WITH 
THIS ACTIVITY. SIMILAR CONVECTION IS ALSO NOTED NEAR 12N98W.

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...THU NIGHT THROUGH THE WEEKEND.

$$
GR/SS