000
AXPZ20 KNHC 230918
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT MAY 23 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 
0900 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 85W N OF 2N. SCATTERED MODERATE TO 
STRONG CONVECTION IS NOTED WITHIN AROUND 90 NM EITHER SIDE OF 
AXIS N OF 8N. PART OF THIS ACTIVITY IS AFFECTING THE PACIFIC 
COAST OF COSTA RICA. A DIFFLUENT PATTERN ALOFT ASSOCIATED WITH 
AN UPPER-LEVEL RIDGE IS HELPING TO INDUCE THE SHOWER/TSTM 
ACTIVITY RELATED TO THE WAVE.  

...ITCZ...
THE ITCZ AXIS IS ALONG 07N77W TO 12N110W TO 09N118W TO 06N140W. 
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS WITHIN 90 NM 
EITHER SIDE OF AXIS E OF 96W. SIMILAR CONVECTION IS NEAR 10N105W.


.DISCUSSION...
NEARLY ZONAL FLOW DOMINATES THE FORECAST AREA N OF 20N. AN 
UPPER-LEVEL RIDGE ALONG 10N-12N COVERS MOST OF THE AREA E OF 
125W. W OF THE RIDGE...THERE IS A TROUGH EXTENDING ALONG 16N130W 
10N135W 05N136W. ABUNDANT MID/UPPER LEVEL MOISTURE IS OBSERVED 
WITHIN THE RIDGE WHILE A NEW SWATH OF MOISTURE IS ENTERING THE 
NW PORTION OF THE FORECAST AREA AHEAD OF A STRONG UPPER-LEVEL 
TROUGH/LOW LOCATED W OF 140W. 

AT THE SURFACE...A 1030 MB HIGH PRES CENTER LOCATED WELL N OF 
AREA EXTENDS A RIDGE SE TO 19N111W. SOUTH OF THE RIDGE...A PAIR 
OF 1008 MB LOW PRES CENTERS REMAIN. ONE IS NEAR 12N123W. PRES 
GRADIENTE BETWEEN THE RIDGE AND THE LOW IS PRODUCING FRESH NE 
TRADE WINDS WITH 8 FT SEAS WITHIN 420 NM NW SEMICIRCLE OF LOW. 
A QSCAT PASS FROM AROUND 0215 UTC SHOWED VERY WELL THE CYCLONIC 
CIRCULATION ASSOCIATED WITH THIS SYSTEM. THE SECOND SFC LOW IS 
SITUATED NEAR 14N112W. CONVECTION ASSOCIATED WITH THIS FEATURE 
HAS DIMINISHED SINCE YESTERDAY...AND UPPER-LEVEL WINDS ARE 
BECOMING LESS CONDUCIVE FOR TROPICAL DEVELOPMENT. WINDS OF 20 KT 
AND SEAS OF 9 FT ARE FOUND WITHIN 120 NM E SEMICIRCLE OF LOW.

LONG PERIOD N SWELLS WILL CONTINUE TO GRADUALLY INVADE THE N 
WATERS MAINLY N OF 28N BETWEEN 120W AND 135W DURING THE NEXT 24 
TO 48 HOURS. 

$$
GR