000
AXPZ20 KNHC 201012
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC MON SEP 20 2010

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 
0930 UTC.

...ITCZ...
MONSOONAL S TO SW FLOW DOMINATES THE DEEP TROPICS ACROSS THE 
AREA...WITH A MONSOON TROUGH EXTENDING FROM 16N103W TO 13N112W 
TO LOW PRES 13N124W 1009 MB TO 11N130W TO 10N140W. SCATTERED 
MODERATE CONVECTION WITHIN WAS NOTED WITHIN 270 NM S OF AXIS E 
OF 110W. SCATTERED TO LOCALLY NUMEROUS ISOLATED STRONG 
CONVECTION WAS NOTED WITHIN 180 NM S OF AXIS W OF 110W. 

...DISCUSSION...

ALOFT...
SW WINDS PREVAIL OVER NW PORTION OF THE FORECAST REGION BETWEEN 
A LONG WAVE TROUGH N THROUGH W OF AREA AND THE SUBTROPICAL RIDGE 
EXTENDING WSW FROM AN ANTICYCLONIC CIRCULATION NEAR 27N118W TO 
BEYOND 20N140W. THIS SYSTEM WILL REMAIN NEARLY STATIONARY 
THROUGH 24 HOURS BEFORE SHIFTING E AND SE TUE THROUGH WED AS A 
S/W TROUGH SHIFTS E INTO THE W COAST OF THE U.S. ANOTHER 
ANTICYCLONE IS CENTERED JUST SE OF BROWNSVILLE TEXAS AND 
DOMINATES THE GULF OF MEXICO AND MOST OF MEXICO. FAVORABLE 
DIVERGENT UPPER LEVEL FLOW SW OF THIS HIGH WAS ENHANCING DEEP 
NOCTURNAL CONVECTION MOVING OFF THE W SLOPES OF THE SIERRA MADRE 
OCCIDENTALES AND SHIFTING W OVER THE MEXICAN COASTAL WATERS. THE 
COMBINATION OF THESE TWO UPPER HIGHS CONTINUES TO PRODUCE A 
GENERAL NE TO E UPPER LEVEL FLOW ACROSS THE AREA S OF 20N...WITH 
DEEP CONVECTION OCCURRING ON THE S SIDE OF THE MONSOON TROUGH 
BETWEEN 112W AND 130W INDUCING STRONG UPPER DIVERGENCE. OTHER 
MODERATE TO STRONG CONVECTION OCCURRING N OF 10N BETWEEN 92W 
AND 102W WAS BEING ENHANCED BY DIFFLUENT FLOW ALOFT.

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 30N125.5W TO 26N132W TO 
25N140W. THE FRONT IS EXPECTED TO DISSIPATE ACROSS NE PORTIONS 
TODAY. 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 121W TO W COAST OF BAJA CALIFORNIA WITH SEAS 
TO 9 FT IN MIXED NW AND SW SWELL. WINDS AND SEAS ARE EXPECTED TO 
DIMINISH THERE IN ABOUT 36 TO 48 HOURS. THE MONSOON TROUGH AND 
ASSOCIATED FLOW MENTIONED ABOVE DOMINATES REST OF THE BASIN AND 
EXTENDS E AND NE INTO CENTRAL AMERICA AND THE FAR SW CARIBBEAN. 
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 UP TO 300 NM S OF THE MONSOON 
TROUGH AXIS...AND ARE PRODUCING SEAS TO 12 FEET BETWEEN 102W AND 
115W. MODEL GUIDANCE SHOWS ISOLATED AREAS OF WINDS 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.

$$
STRIPLING