000
AXPZ20 KNHC 211540
TWDEP 

TROPICAL WEATHER DISCUSSION      
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT JUL 21 2007

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 
1500 UTC.

...TROPICAL WAVES...
NO TROPICAL WAVES ARE CURRENTLY OBSERVED IN THE EASTERN PACIFIC.

...ITCZ...
ITCZ AXIS ALONG 8N81W 11N96W 11N104W 13N114W 6N140W. SCATTERED 
MODERATE CONVECTION WITHIN 90 NM N OF AXIS E OF 89W. SCATTERED 
MODERATE TO STRONG CONVECTION FROM 9N TO 15N BETWEEN 99W AND 106W.

...DISCUSSION...
E OF 110W...
1009 MB SURFACE LOW ANALYZED SW OF GULF OF TEHUANTEPEC NEAR 11N100W. 
THE SYSTEM IS MOVING AWAY FROM A SMALL UPPER LEVEL TROUGH ALONG 90W 
AND ENCOUNTERING LESS VERTICAL SHEAR. CONSEQUENTLY CONVECTION NEAR 
THE LOW HAS INCREASED...BUT LACKS ORGANIZATION OR STRUCTURE AT THIS 
TIME. THE ECMWF AND UKMET MODELS ARE MOST AGGRESSIVE IN DEVELOPING 
THIS LOW...BUT EVEN THEN...INTENSIFICATION IS SLOW TO OCCUR. GFS AND 
NOGAPS MAINTAIN A WEAK CIRCULATION...BUT NO CYCLOGENESIS. ELSEWHERE 
AN UPPER RIDGE IN THE SRN CARIBBEAN EXTENDS WWD ACROSS COSTA RICA 
AND NICARAGUA TO 10N90W. UPPER DIFFLUENCE ON THE S SIDE OF THE RIDGE 
IS HELPING ITCZ CONVECTION TO DEVELOP.

W OF 110W...
THE PERSISTENT TROUGH FROM SOUTHERN BAJA TO NEAR 9N125W HAS WEAKENED
CONSIDERABLY AND NOW APPEARS TO BE SPLITTING INTO A WEAK TROUGH ALONG
THE BAJA PENINSULA AND A DIFFUSE LOW LEVEL CIRCULATION NEAR 10N122W.
WITH THE SLY FLOW BREAKING DOWN...THE ANOMALOUS NORTHWARD EXTENSION 
OF THE ITCZ THE PAST FEW DAYS HAS PRETTY MUCH DISAPPEARED. CLOUDS 
AND SHOWERS ARE DECREASING ALONG THE TROUGH AXIS AS WELL. AN UPPER 
LOW LOCATED JUST W OF BAJA CALIFORNIA NEAR 26N115W IS HELPING PULL 
TROPICAL MOISTURE NWD INTO NW MEXICO AND THE SW U.S. BENIGN TRANQUIL
CONDITIONS ELSEWHERE. AN UPPER TROUGH ALONG THE W COAST OF THE U.S. 
HAS WEAKENED THE SUBTROPICAL RIDGE AND WEAKENED THE NE TRADE WINDS.

$$
MUNDELL