000
AXPZ20 KNHC 301558
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC TUE SEP 30 2008

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1515 UTC.

...SPECIAL FEATURES...

LOW PRES 1008 MB IS LOCATED AT 10N97W...ALONG THE INTERSECTION 
OF THE ITCZ AND A TROPICAL WAVE N OF 07N ALONG 97W MOVING W AT 7 
KT. A QUIKSCAT PASS SHOWED HORIZONTAL VORTICITY AROUND THE LOW 
BEING ENHANCED BY STRONG NE WINDS THROUGH THE GULF OF 
TEHUANTEPEC THAT CONTINUED SW TO THE SOUTH OF THE LOW AND ITCZ.  
THE LOW IS CENTERED ON THE EASTERN EDGE OF AN UPPER RIDGE THAT 
IS CENTERED JUST S OF BAJA CALIFORNIA...ALLOWING FOR EASTERLY 
SHEAR OVER THE AREA. THUS THE MAJORITY OF THE CONVECTION IS W OF 
THE LOW CENTER. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION 
IS FROM 07N TO 13N BETWEEN 96W AND 102W...AND FROM 11N TO 13N 
BETWEEN 95W AND 97W. THE SHEAR IS WEAK ENOUGH HOWEVER TO ALLOW 
FOR FURTHER DEVELOPMENT AND GLOBAL MODELS CONTINUE TO SUGGEST 
THAT THIS FEATURE WILL HOLD TOGETHER AS IT MOVES IN A GENERAL 
WESTWARD DIRECTION OVER THE NEXT FEW DAYS WITH A MEDIUM 
POTENTIAL OF IT UNDERGOING SOME SLOW DEVELOPMENT.

...TROPICAL WAVES...

TROPICAL WAVE ALONG 90W/91W N OF 06N IS MOVING W ABOUT 10 KT. 
THE ITCZ TRAVERSES THE WAVE AXIS AS FAR N AS 12N WITH SW SURFACE 
FLOW...THAT DISRUPTS THE USUAL INVERTED-V SURFACE FLOW OF THE 
WAVE. SCATTERED MODERATE CONVECTION IS HOWEVER ON THE WAVE AXIS 
FROM 08N TO 11N BETWEEN 88W AND 93W.     

TROPICAL WAVE IS EMBEDDED WITHIN A BROAD LOW PRES AREA FROM 10N 
TO 20N ALONG 116W/117W. AN ASSOCIATED WEAK SURFACE LOW PRES AREA 
1008 MB IS CENTERED NEAR 14N114W. THE WAVE/LOW COMPLEX IS MOVING 
W AT 10 KT. 

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 11N86W TO 12N96W TO 11N100W TO 
13N114W TO 10N125W TO 12N137W TO 10N140W. BESIDES THE CONVECTION 
MENTIONED IN THE SPECIAL FEATURE AND TROPICAL WAVE SECTIONS... 
SCATTERED MODERATE CONVECTION IS S OF PANAMA FROM 04N TO 07N 
BETWEEN 78W AND 83W. SCATTERED MODERATE CONVECTION IS FROM 14N 
TO 16N BETWEEN 106W AND 108W. SIMILAR CONVECTION IS FROM 08N TO 
12N BETWEEN 108W AND 120W...AND FROM 07N TO 10N BETWEEN 129W AND 
139W.

...DISCUSSION...

E OF 110W...20 TO 30 KT WINDS ACROSS THE GULF OF TEHUANTEPEC AND 
CONTINUE SW TO THE LOW NEAR 11N97W. MOST GLOBAL MODELS INDICATE 
THIS LOW TO DEVELOP...AND FOR THE GULF OF TEHUANTEPEC TO PERSIST 
FOR AT LEAST THE NEXT 2 TO 3 DAYS. ELSEWHERE S OF THE ITCZ 
MODERATE TO FRESH S TO SW CROSS EQUATORIAL FLOW PERSISTS. EXPECT 
WEAKENING EAST SHEAR OVER THE LOW NEAR 11N97W. ALSO EXPECT 
CONSIDERABLE POTENTIAL PRECIPITATION OVER THE AREA N OF 05N.    

W OF 110W...DIVERGENT SE FLOW ALOFT AROUND THE SOUTHERN EDGE OF 
AN UPPER ANTICYCLONE NEAR 20N110W IS ENHANCING CONVECTION ALONG 
THE TROPICAL WAVE ALONG 116W/117W MENTIONED ABOVE. THE 
ASSOCIATED LOW IS NOT EXPECTED TO DEVELOP MUCH MORE...AS IT 
MOVES INTO AN AREA OF MORE STABLE AIR AND COOLER WATER. 
ELSEWHERE DEEP LAYER MOISTURE REMAINS MINIMAL OUTSIDE OF THE 
ITCZ. A WEAK 1010 MB SURFACE LOW IS CENTERED ALONG THE ITCZ NEAR 
12N137W. THIS LOW WILL CONTINUE TO FILL AS IT MOVES W. FURTHER 
TO THE NORTH...A VIGOROUS UPPER TROUGH CONTINUES TO DIG INTO 
FORECAST AREA ALONG ROUGHLY 140W N OF 15N. AN ASSOCIATED COLD 
FRONT EXTENDS FROM 32N133W TO 25N140W. SCATTEROMETER AND SHIP 
OBSERVATION SHOW A BAND OF 20 TO 25 KT SW WINDS WITHIN 150 NM E 
OF THE FRONT. THESE WINDS ARE EXPECTED TO GRADUALLY DIMINISH 
THROUGH THE NEXT COUPLE OF DAYS AS THE SUPPORTING UPPER DYNAMICS 
LIFT OUT TO THE NW. SHIP OBSERVATIONS CONFIRM THE WAVEWATCH 
MODEL SHOWING LONG PERIOD NW SWELL TO 11 FT...EXPECTED TO 
CONTINUE TO PROPAGATE INTO THE AREA GENERALLY N OF 15N W OF 125W 
THROUGH THE REMAINDER OF THE WEEK. 

$$
FORMOSA