000
AXPZ20 KNHC 251540
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC TUE AUG 25 2009

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 
1400 UTC.

...SPECIAL FEATURE...

TROPICAL STORM IGNACIO 18.6N119.3W AT 1500 UTC AND MOVING W-NW 
AT 10 KT. MAXIMUM SUSTAINED WINDS 40 KT WITH GUSTS TO 50 KT. 
CURRENTLY...UPPER LEVEL OUTFLOW REMAINS RESTRICTED IN THE 
NORTHERN SEMICIRCLE OF IGNACIO...BUT SHEAR SHOULD RELAX SOMEWHAT 
OVER THE NEXT 24 HOURS AND THE SYSTEM WILL REMAIN OVER 
SUFFICIENTLY WARM WATER DURING THIS TIME. THE CURRENT FORECAST 
DOES NOT CALL FOR IGNACIO TO BECOME A HURRICANE BEFORE IT 
ENCOUNTERS COOLER WATERS AROUND 36 HOURS AND BEGINS TO WEAKEN. 
ADDITIONAL INFORMATION CAN BE FOUND UNDER AWIPS/WMO HEADERS 
MIATCMEP3/WTPZ23 KNHC.

A TROPICAL WAVE MOVING W AT 15-20 KT LIES ALONG 83W N OF 06N. A 
WELL-DEFINED MID-LEVEL CIRCULATION ASSOCIATED WITH THIS TROPICAL 
WAVE LIES OVER SOUTHERN NICARAGUA. SCATTERED STRONG CONVECTION 
CAN BE FOUND OVER NICARAGUA WITHIN 150 NM OF THE WAVE FROM 11N 
TO 15N. SCATTERED MODERATE CONVECTION CAN BE FOUND ON THE SW 
SIDE OF THE WAVE WITHIN 75 NM N AND 90 NM S OF THE ITCZ AXIS E 
OF 87W.
 
...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG 09N84W TO 08N95W TO 
13N110W TO 13N122W TO 10N140W. SCATTERED MODERATE CONVECTION CAN 
BE FOUND WITHIN 75 NM N AND 90 NM S OF THE ITCZ AXIS E OF 87W 
AND BETWEEN 102W AND 105W WITHIN 210 NM N OF THE ITCZ AXIS.  
SCATTERED MODERATE ISOLATED STRONG CONVECTION LIES WITHIN 90 NM 
N AND 45 NM S OF THE ITCZ AXIS BETWEEN 129W AND 133W.

...DISCUSSION...

N OF 20N...
A RIDGE/TROUGH/RIDGE UPPER PATTERN IS EVIDENT ACROSS THE 
REGION...WITH TROPICAL STORM IGNACIO BUTTING UP AGAINST THE SW 
SIDE OF THE EASTERN RIDGE THAT EXTENDS FROM AN ANTICYCLONE NEAR 
22N115W TO NEAR 20N126W. IGNACIO IS FORECAST TO PROCEEDED N AND 
W TOWARD THE TROUGH AXIS CURRENTLY ALONG 130W...DRIVING A LARGER 
WEDGE BETWEEN THE EASTERN RIDGE AND THE UPPER LEVEL ANTICYCLONE 
CENTERED NEAR 22N140W. A VAST AREA OF DRY AIR ALOFT CAN BE FOUND 
W OF 125W AS WELL N OF IGNACIO IN THE AREA N OF 24N E OF 
125W...RESULTING IN GENERALLY FAIR WEATHER CONDITIONS. SURFACE 
HIGH PRES IS CENTERED N OF THE AREA NEAR 33N135W. NE 15-20 KT 
TRADES EXIST ACROSS THE NW CORNER BUT ARE EXPECTED TO DIMINISH 
BELOW 20 KT LATER TODAY AS THE RIDGE WEAKENS. 

S OF 20N...
PRECIPITABLE WATER VALUES OVER 2 INCHES ARE POOLED ALONG THE 
ITCZ AXIS E OF 120W AND THIS REGION COINCIDES WITH AN AREA OF 
MODERATE UPPER LEVEL DIFFLUENCE. A LOW LEVEL CIRCULATION 
EMBEDDED IN THE ITCZ WAS EVIDENT ON THE 0314 UTC QUIKSCAT PASS 
NEAR 11N133W. THERE IS STRONG LOW LEVEL MOISTURE CONVERGENCE 
WITH THIS FEATURE AND SCATTERED MODERATE ISOLATED STRONG 
CONVECTION LIES WITHIN 90 NM N AND 45 NM S OF THE ITCZ AXIS 
BETWEEN 129W AND 133W ASSOCIATED WITH THIS FEATURE. SOME OF THE 
NUMERICAL GUIDANCE DEVELOPS THIS SYSTEM INTO A CLOSED LOW LEVEL 
CIRCULATION WITH WINDS TO 25 KT...BUT THE OFFICIAL FORECAST 
LEANS TOWARD THE WEAKER MODEL CONSENSUS WHICH KEEPS THE SYSTEM 
NEARLY STATIONARY WITH WINDS TO 20 KT AND SEAS TO 8 FT.

THE 1236 UTC QUIKSCAT PASS JUST ARRIVED AND SHOWS A SOLID AREA 
OF WINDS TO 30 KT WITHIN 90 NM S-SW OF THE GULF OF TEHUANTEPEC. 
THE NUMERICAL MODEL GUIDANCE IS RUNNING LOW WITH THE WINDS 
HERE...AND BELIEVE IT IS STILL LOW IN THE FORECAST PERIOD. WINDS 
ARE EXPECTED BE MAINTAINED ABOVE 20 KT AS THE TROPICAL WAVE 
CURRENTLY ALONG 83W APPROACHES.

$$
SCHAUER CLARK