000
AXPZ20 KNHC 212120
TWDEP 

TROPICAL WEATHER DISCUSSION      
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SAT JUL 21 2007

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...SPECIAL FEATURE...

A 1009 MB LOW IS CENTERED NEAR 12N103W...OR ABOUT 360 NM SW OF 
ACAPULCO MEXICO...MOVING W NEAR 15 KT. THE LOW HAS A RATHER 
LARGE CIRCULATION WHICH EXTENDS AT LEAST 400 NM AWAY FROM THE 
CENTER. VISIBLE SATELLITE IMAGERY SHOWS A WELL-DEFINED 
CONVECTIVE BAND OVER THE WRN SEMICIRCLE...A DISORGANIZED CLUSTER 
OF CONVECTION E OF THE CENTER...AND ADDITIONAL CONVECTIVE 
ELEMENTS DEVELOPING NEAR THE CENTER. BECAUSE OF THE IMPROVING 
SIGNATURE OF THE CONVECTIVE PATTERN AND THE RELATIVELY LOW SHEAR 
OVER THE SYSTEM AT THE MOMENT...TROPICAL CYCLONE DEVELOPMENT IS 
POSSIBLE WITHIN THE NEXT 48 HRS. SCATTERED MODERATE/ISOLATED 
STRONG CONVECTION EXTENDS UP TO 300 NM AWAY FROM THE CENTER OF 
THE LOW.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 8N77W 13N100W THEN 17N113W 10N122W 
5N140W. SCATTERED MODERATE CONVECTION FROM 5N-9N E OF 88W. 
SCATTERED MODERATE WITHIN 90 NM OF AXIS BETWEEN 118W-128W. 
ISOLATED SHOWERS/TSTMS WITHIN 60 NM OF AXIS W OF 130W.

...DISCUSSION...

E OF 110W...
SEE SPECIAL FEATURES FOR DISCUSSION ON LOW PRES SW OF THE GULF 
OF TEHUANTEPEC NEAR 12N103W. FOR THE MOST PART...THE UPPER LEVEL 
PATTERN OVER THE FAR E TROPICAL PACIFIC IS NOT DOMINATED BY ANY 
SIGNIFICANT FEATURES. A LARGE MID/UPPER LOW IS LOCATED NEAR THE 
YUCATAN CHANNEL AND TWO MID/UPPER LEVEL HIGHS ARE SITUATED OVER 
FAR NRN MEXICO AND THE SW CARIBBEAN. THESE THREE FEATURES ARE 
DRIVING PRIMARILY NE/E FLOW ALOFT OVER THE FAR E PACIFIC 
WATERS...AND ALSO SUPPORTING UPPER LEVEL DIFFLUENCE FROM ACROSS 
SE PARTS OF CENTRAL AMERICA TO THE LOW NEAR 12N103W. AS A 
RESULT...SCATTERED CONVECTION HAS BEEN PULSING ALONG THE ITCZ E 
OF 90W AND HAS ALSO BEEN ON THE INCREASE NEAR THE AFOREMENTIONED 
LOW. SCATTERED TSTMS HAVE ALSO FORMED OVER THE COASTAL MOUNTAINS 
FROM EL SALVADOR NW TO NEAR ACAPULCO MEXICO...AND THE STEERING 
FLOW FROM THE N WILL PUSH THIS ACTIVITY OVER THE BEACHES AND 
ADJACENT COASTAL WATERS THROUGH THE EVENING.

W OF 110W...
A WEAK UPPER LEVEL HEIGHT PATTERN IS IN CONTROL OVER THE W PART 
OF THE DISCUSSION AREA AND THERE ARE FEW SIGNIFICANT WEATHER 
PRODUCERS AT THE MOMENT. THE UPPER LEVEL HIGH OVER NRN MEXICO 
NEAR 27N105W AND A MID/UPPER LOW ALONG THE W COAST OF BAJA 
CALIFORNIA NEAR 28N115W ARE PULLING DEEP TROPICAL MOISTURE NWD 
TOWARDS THE MOUTH OF THE GULF OF CALIFORNIA. HOWEVER...THE 
ELONGATED NWD EXTENSION OF THE ITCZ WHICH HAS BEEN IN PLACE 
OVER THE PAST SEVERAL DAYS IS NOW WEAKENING...AND THE LOW-LEVEL 
CONVERGENCE IS NO LONGER STRONG ENOUGH TO SUPPORT CONVECTION 
THAT FAR N. STILL...A FEW TSTMS MAY FORM ALONG THE E SHORE OF 
THE GULF OF CALIFORNIA THIS EVENING. ELSEWHERE...THE UPPER RIDGE 
ALONG 30N HAS BEEN SEVERELY WEAKENED BY A LARGE CYCLONIC GYRE 
OVER THE GULF OF ALASKA AND A MORE SUBDUED INVERTED TROUGH 
LOCATED ALONG 136W S OF 24N. AS A RESULT...THE SUBTROPICAL SFC 
RIDGE IS ALSO WEAKENED AND THE ELY TRADES ARE BARELY REACHING 20 
KT NEAR 140W.

$$
BERG