000
AXPZ20 KNHC 200248
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC MON SEP 20 2010

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.

...ITCZ...
MONSOONAL S TO SW FLOW NOT DESCRIBED BY THE ITCZ DOMINATES THE 
DEEP TROPICS ACROSS THE AREA...WITH A MONSOON TROUGH EXTENDING 
FROM LOW PRES 18N106W 1003 MB TO 12N110W TO LOW PRES 13N124W 
1008 MB TO 09N140W. SCATTERED MODERATE CONVECTION IS WITHIN 50 
NM EITHER SIDE OF TROUGH BETWEEN 114W AND 121W. 

...DISCUSSION...

ALOFT...
SW WINDS PREVAIL OVER NW PORTION OF THE FORECAST REGION BETWEEN 
LONG WAVE TROUGH W OF AREA AND THE SUBTROPICAL RIDGE EXTENDING 
WSW FROM AN ANTICYCLONIC CIRCULATION NEAR 27N117W TO BEYOND 
20N140W. THIS SYSTEM WILL REMAIN NEARLY STATIONARY. ANOTHER 
ANTICYCLONE IS CENTERED NEAR BROWNSVILLE TEXAS. FAVORABLE 
DIVERGENT UPPER LEVEL FLOW SW OF THIS FEATURE IS ENHANCING DEEP 
CONVECTION ASSOCIATED WITH THE SURFACE MONSOON TROUGH E OF 112W. 
IN ADDITION...UPPER LEVEL WINDS REMAIN QUITE STRONG ON THE 
SOUTHERN PERIPHERY OF THIS ANTICYCLONE PREVENTING MOST OF THE 
LOW PRESSURE AREAS FROM DEVELOPING INTO LOWS WITH POTENTIAL TO 
BECOME TROPICAL CYCLONES. MODEL GUIDANCE SHOWS WINDS ALOFT 
DECREASING SOMEWHAT OVER THE NEXT COUPLE OF DAYS...WHICH COULD 
ALLOW A LOW CENTERED NEAR 18N106W TO BECOME A TROPICAL CYCLONE. 
THERE IS A MEDIUM CHANCE OF THIS SYSTEM BECOMING A TROPICAL 
CYCLONE DURING THE NEXT 48 HOURS.

SURFACE...
A WEAKENING COLD FRONT EXTENDS FROM 32N128W TO 25N140W. THE 
FRONT WILL DISSIPATE MON. SCATTEROMETER AND ALTIMETRY DATA SHOWS 
WINDS LESS THAN 20 AND 7-8 FT SEAS ASSOCIATED WITH FRONT. WEAK 
RIDGING AHEAD OF THE FRONT COMBINED WITH LOW PRES OVER NW MEXICO 
AND BAJA CALIFORNIA IS PRODUCING 20-25 KT NW WINDS N OF 22N E OF 
120W TO W COAST OF BAJA CALIFORNIA. WINDS AND SEAS ARE EXPECTED 
TO DIMINISH IN ABOUT 36 TO 48 HOURS. MONSOON TROUGH MENTIONED 
ABOVE IN ITCZ SECTION DOMINATES REST OF THE BASIN. SCATTEROMETER 
DATA SHOWS FRESH S-SW WINDS SOUTH OF THE TROUGH AXIS COVERING AS 
FAR WEST AS 130W. 

MARINE...
FRESH TO STRONG SW WINDS PERSIST WITHIN 150 NM S OF THE MONSOON 
TROUGH AXIS...AND ARE PRODUCING SEAS TO NEAR 13 FEET BETWEEN 
102W AND 108W. MODEL GUIDANCE SHOWS WINDS INCREASING TO NEAR 30 
KT IN ABOUT 48 HOURS IN THIS AREA. LARGE SWELLS WILL CONTINUE TO 
PROPAGATE FROM SW TO NE OVER A BROAD PORTION OF THE AREA THROUGH 
MONDAY.

$$
GR/DM