000
AXPZ20 KNHC 100922
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT OCT 10 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 
0915 UTC.

...SPECIAL FEATURE... 

A BROAD AREA OF LOW PRES NEAR 18N106W HAS MOVED LITTLE OVER THE 
PAST 24 HOURS. CONVECTION AROUND THE LOW PRES HAD DIED ALMOST 
ENTIRELY SEVERAL HOURS AGO. LATEST SATELLITE IMAGES SHOW 
CLUSTERS OF THUNDERSTORM REFORMING IN THE SOUTHWEST QUADRANT OF 
THE LOW WHERE SW WINDS TO THE SOUTH OF THE ITCZ ARE CONVERGING 
WITH NW WINDS AROUND THE PERIPHERY OF THE LOW. A 0130Z QUIKSCAT 
PASS SHOWED A SMALL AREA OF WINDS TO 20 KT ON THE N SIDE OF THE 
LOW. OTHERWISE...WINDS REMAIN FAIRLY LIGHT IN ALL QUADRANTS 
OUTSIDE OF CONVECTION. A MID TO UPPER TROUGH THAT WAS THE MAIN 
SUPPORT FOR THE LOW HAS LIFTED OUT TO THE NE...REPLACED BY DEEP 
LAYER DRY WESTERLY WINDS ON THE BACK SIDE OF THE TROUGH. THIS IS 
SHUNTING THE MAIN MOISTURE TO THE EAST AND KEEPING THE LOW 
NEARLY STATIONARY. THE LOW WILL MAKE SLOW PROGRESS NW TO N TO 
THE SOUTH OF CABO SAN LUCAS OVER THE NEXT COUPLE OF DAYS AS A 
PAIR OF WEAK SHORT WAVE TROUGHS MIGRATE EASTWARD TO THE NORTH OF 
THE LOW. WHILE GLOBAL MODELS ARE IN FAIR AGREEMENT REGARDING THE 
TRACK OF THE LOW...THERE REMAINS SOME DISCORD OVER WHETHER THE 
LOW WILL DEVELOP SIGNIFICANTLY THROUGH SUNDAY. THERE IS MEDIUM 
CHANCE...30 TO 50 PERCENT THAT THE LOW MAY FORM INTO A TROPICAL 
CYCLONE AS IT SHIFTS NW TO N. AT ANY RATE...INTERESTS ALONG THE 
MEXICAN COAST NEAR MANZANILLO SHOULD BE AWARE OF THE POTENTIAL 
FOR HEAVY RAINFALL IF CONVECTION ALONG THE EAST SIDE OF THE 
STORM REDEVELOPS.

...TROPICAL WAVE...

A TROPICAL WAVE ALONG 89W N OF 09N IS MOVING WEST AT 10 TO 15 
KT. THIS WAVE IS INTERACTING WITH A WELL DEFINED UPPER LOW NEAR 
14N92W. DIVERGENCE ASSOCIATED WITH THE UPPER LOW ALONG WITH 20 
KT SW FLOW TO THE SOUTH OF THE ITCZ IS ENHANCING SCATTERED 
MODERATE CONVECTION ALONG THE WAVE...WITH ISOLATED STRONG 
CONVECTION ALONG THE NICARAGUAN COAST AIDED BY LATE NIGHT 
DRAINAGE FLOW.

...ITCZ...

THE ITCZ AXIS WAS CENTERED ALONG 09N85W TO 10N89W TO 09N93W TO 
13N105W TO 13N132W TO 09N140W. SCATTERED STRONG CONVECTION NOTED 
WITHIN 120 NM N OF AXIS ALONG NICARAGUAN COAST. SCATTERED 
MODERATE CONVECTION WITHIN 60 NM S OF AXIS BETWEEN 85W AND 90W. 
SCATTERED MODERATE CONVECTION WITHIN 120 NM S OF AXIS BETWEEN 
100W AND 110W. SCATTERED MODERATE CONVECTION WITHIN 120 NM 
EITHER SIDE OF AXIS BETWEEN 130W AND 135W.

...DISCUSSION...

AN ELONGATED MID TO UPPER LEVEL RIDGE AXIS IS ORIENTED EAST TO 
WEST ALONG 17N. A SHORT WAVE TROUGH EXTENDING FROM NORTHERN 
CALIFORNIA TO 23N135W IS MOVING EASTWARD TO THE NORTH OF THE 
RIDGE. SUBSIDENT NORTHERLY FLOW ON THE EAST SIDE OF THE UPPER 
RIDGE IS MAINTAINING FAIRLY DRY AIR N OF THE ITCZ BETWEEN 115W 
TO 125W. DIVERGENT FLOW ALOFT BETWEEN THE SHORT WAVE TROUGH AND 
THE WESTERN EDGE OF THE UPPER RIDGE IS PROVIDING EXHAUST TO 
ENHANCE CONVECTION ALONG THE ITCZ BETWEEN 130W AND 135W. A WEAK 
SURFACE TROUGH IS ANALYZED WITHIN THIS CONVECTION NEAR 133W. A 
03Z QUIKSCAT PASS SHOWED PERSISTENT FRESH TRADES BETWEEN THE 
ITCZ AND 20N ON THE SOUTHERN PERIPHERY OF A BROAD SURFACE RIDGE 
N OF THE AREA. A 0130Z ASCAT PASS SHOWED 20 KT NORTHERLY FLOW 
BETWEEN THE EASTERN EDGE OF THE SURFACE RIDGE AND THE NORTHERN 
BAJA COAST. THESE WINDS WILL DIMINISH THROUGH TODAY AS THE 
RIDGE WEAKENS AHEAD OF A COLD FRONT APPROACHING THE AREA FROM 
THE CENTRAL PACIFIC. THE FRONT WILL REACH A POSITION FROM 
30N135W TO 22N140W.

LONG PERIOD NE SWELL IN THE AREA OF TRADES ROUGHLY FROM 10N TO 
20N W OF 120W WILL DECAY THROUGH TONIGHT...JUST AHEAD OF THE 
ARRIVAL OF NW SWELL TO 10 FT PUSHES INTO THE DISCUSSION AREA 
SUNDAY BEHIND THE FRONT.

$$
CHRISTENSEN