000
AXPZ20 KNHC 291605
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU OCT 29 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 
1545 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE WAS CENTERED ALONG 10N86W TO 
13N97W TO 11N112W TO 11N120W TO 10N131W TO 9N140W. SCATTERED 
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM S OF THE 
AXIS BETWEEN 94W-98W...AND BETWEEN 134W-137W. SCATTERED MODERATE
CONVECTION IS WITHIN 180 NM S OF THE AXIS BETWEEN 100W-107W.

...DISCUSSION...

A SHARPENING DEEP LAYERED LONGWAVE TROUGH ACROSS WRN N AMERICA 
WAS ALONG 110W...THEN EXTENDED SW TO 22N120W TO 19N126W AND
TO AN ELONGATED MID/UPPER LEVEL CYCLONIC CIRCULATION NEAR 
15N134W. A JET STREAM BRANCH IS ALONG THE SOUTHERN PERIPHERY OF
THE TROUGH FROM 12N135W NE TO 17N124W TO 20N115W...AND CONTINUES
NE TO ACROSS N CENTRAL MEXICO TO OVER EASTERN TEXAS. THE TROUGH 
IS FORECAST TO BEGIN TO SHIFT E ACROSS THE U.S. TONIGHT AND LIFT 
UP AND OVER A FLATTENING RIDGE ACROSS THE GLFMEX AND SE U.S. 
THROUGH THE WEEKEND. TO THE W OF THE TROUGH...A VERY SHARP AND 
LARGE UPPER RIDGE WITH ITS CREST SPILLING SE IS ALONG ROUGHLY 
ALONG 145W.

THE SHARPENING LONG WAVE TROUGH ACROSS THE WRN U.S. HAS ALLOWED 
FOR A STRONG NLY FLOW TO DIVE ALONG THE W COAST OF THE U.S. AND 
INTO THE N HALF OF THE FORECAST AREA. UPPER LEVEL CONFLUENCE 
INTO THE BACKSIDE OF THE TROUGH IS RESULTING MODERATE TO STRONG 
SUBSIDENCE AND VERY STABLE AIR ACROSS THIS AREA NW OF THE ABOVE 
JET STREAM BRANCH. SATELLITE IMAGERY SHOWED PATCHES OF BROKEN TO 
OVERCAST STRATOCUMULUS MOVING SW TO THE N OF 15N AND W OF 114W. 
AT THE SURFACE...A 1028 MB HIGH CENTER N OF THE AREA NEAR 
37N135W EXTENDS A RIDGE SE TO NEAR 23N123W. THE TIGHT PRES 
GRADIENT TO THE E OF THE RIDGE IS BRINGING N WINDS OF 20-25 KT N 
OF 27N E OF 127W WITH SEAS OF 10-16 FT. THE COLD AIR ADVECTION 
AND PRESSURE GRADIENT INDUCED BY THIS SYNOPTIC PATTERN WILL 
GRADUALLY RELAX OVER THE NEXT 12 TO 48 HOURS AS THE TROUGH 
SHIFTS E ACROSS THE U.S. WHICH WILL CAUSE THE FRESH NE TRADES TO 
SHIFT TO W OF 122W BY SAT. THE MIX OF NLY AND NW SWELL FROM THIS 
EVENT WILL PUSH 8 FT SEAS S AND SE AND ACROSS 9N SATURDAY 
MORNING...WITH SEAS TO 8 FT.

OVER THE EASTERN PORTION...AN UPPER RIDGE CONTINUES FROM THE 
ITCZ ALONG 105W...NE ACROSS THE SE GLFMEX...WHILE A TUTT LOW HAS 
GRADUALLY RETROGRADED SW INTO THE SW CARIBBEAN ALONG 79W. 
DIFFLUENCE ALOFT INDUCED BY THIS PATTERN IS MAINTAINING ACTIVE 
CONVECTION ACROSS THIS PORTION OF THE EPAC...AS THE MONSOONAL 
GYRE DOMINATES E OF 110W. AN ELONGATED TROUGH CONTINUES THIS 
MORNING FROM 17N101W TO 13N101W TO 9N109W. SCATTERED STRONG
CONVECTION IS WITHIN 150 NM E OF THE TROUGH N OF 14N...AND 
WITHIN 30 NM OF 17N103W. AS THE TROUGH SHIFTS E AND LIFTS OUT 
OVER THE WEEKEND...GLOBAL MODELS RESPOND BY SUGGESTING THE 
OPPORTUNITY FOR BETTER ORGANIZATION OF A LOW ACROSS THIS 
AREA...WITH POTENTIAL FOR TROPICAL CYCLOGENESIS BETWEEN 90W AND 
105W OVER THE NEXT SEVERAL DAYS. GOOD INFLOW OF 20-25 KT INTO 
THE S SIDE OF THIS CYCLONIC GYRE WILL CONTINUE S OF THE ITCZ 
DURING THE NEXT FEW DAYS...MAINTAINING SEAS UP TO 8 FT.

$$
AGUIRRE