000
AXPZ20 KNHC 280251
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SAT AUG 28 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 
0115 UTC.

...SPECIAL FEATURES...

TROPICAL STORM FRANK IS CENTERED NEAR 19.8N 112.6W MOVING NW OR 
325 DEG AT 6 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 999 MB. 
MAXIMUM SUSTAINED WINDS ARE 45 KT WITH GUSTS TO 55 KT. TROPICAL 
STORM FORCE WINDS EXTEND OUTWARD UP TO 40 NM FROM THE CENTER. 
SCATTERED MODERATE CONVECTION IS DISPLACED WITHIN 180 NM W 
QUADRANT OF ITS EXPOSED CENTER. FRANK HAS ENCOUNTERED EASTERLY 
SHEAR. IT IS FORECAST TO DIMINISH TO A TROPICAL DEPRESSION ON 
SAT AND TO A REMNANT LOW ON SUN AS IT TAKES A MORE NORTHEASTERLY 
TURN. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS 
MIATCMEP4/ WTPZ24 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE N OF 08N ALONG 93W MOVING W AROUND 15 KT. 
SCATTERED MODERATE CONVECTION LIES WITHIN 210 NM W OF THE WAVE 
FROM 11N TO 14N AND WITHIN 120 NM E OF THE WAVE N OF 13N TO THE 
COAST OF GUATEMALA. INLAND...SCATTERED MODERATE CONVECTION ALSO 
LIES OVER THE BORDER OF GUATEMALA AND HONDURAS AS WELL AS ALONG 
THE WAVE AXIS OVER SOUTHERN MEXICO.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE AXIS IS ANALYZED FROM 10N84W 
TO 06N90W TO 07N107W THEN RESUMES NEAR 11N112W TO 09N120W TO 
11N130W TO 08N140W. NO SIGNIFICANT CONVECTION CURRENTLY LIES 
ALONG THE ITCZ AXIS.

...DISCUSSION...

WATER VAPOR IMAGERY SHOWS MODERATE SUBSIDENCE AND DRIER AIR 
ALOFT OVER A LARGE PORTION OF THE AREA NW OF A LINE FROM 27N113W 
TO 13N140W. AN UPPER LEVEL ANTICYCLONE LIES OVER THE GULF OF 
MEXICO AND EXTENDS A RIDGE W TO 23N113W. DIFFLUENCE ALOFT 
ASSOCIATED WITH THIS RIDGE AXIS IS ENHANCING CONVECTION OVER THE 
SIERRA MADRE OCCIDENTAL MOUNTAINS E OF MAZATLAN. A SECOND 
ANTICYCLONE LIES NEAR 23N133W AND EXTENDS A RIDGE E TO 24N123W.
BETWEEN THESE RIDGE AXES LIES AN UPPER TROUGH FROM 30N118W TO 
23N120W. THIS TROUGH IS MOVING INTO THE LEADING EDGE OF A DEEP 
LAYERED TROUGH THAT IS CURRENTLY PUSHING INTO THE WESTERN CONUS. 
THIS COMBINED BROAD TROUGHING IS RESPONSIBLE FOR STEERING FRANK 
NORTHWARD INTO COOLER WATER. THE DEEP LAYER TROUGH WILL DRIVE A 
COLD FRONT THROUGH THE U.S. GREAT BASIN OVER THE NEXT FEW DAYS. 
THE PRES GRADIENT BETWEEN THIS TROUGHING AND THE SUBTROPICAL 
RIDGE IS GENERATING WINDS OVER 20 KT OFF THE CALIFORNIA COAST 
AND THE ASSOCIATED SWELL IS MOVING INTO N WATERS WHERE SEAS ARE 
AS HIGH AS 9 FT. EXPECT WINDS TO 20 KT AND CONTINUED N SWELL 
OVER FAR N WATERS OVER THE NEXT FEW DAYS. THE SUBTROPICAL RIDGE 
CURRENTLY LIES FROM 00N130W TO 23N116W. 

MEAN TROUGHING WILL BUILD OVER WESTERN NORTH AMERICA AS FRANK IS 
FORCED NORTHWARD AND THE TROPICAL WAVE CURRENTLY ALONG 93W 
PROGRESSES W. IN TURN...THE PRES GRADIENT BETWEEN THIS MEAN 
TROUGHING AND HIGHER PRES S OF THE ITCZ WILL BUILD. SW WINDS ARE 
EXPECTED TO INCREASE TO 20 KT IN THE REGION FROM 03N TO 10N 
BETWEEN 90W AND 110W OVER THE WEEKEND BECAUSE OF THE 
STRENGTHENED PRES GRADIENT. SOME OF THE MODEL GUIDANCE HINT AT 
THE DEVELOPMENT OF A LOW PRES SYSTEM JUST N OF THIS REGION AND S 
OF TEHAUNTEPEC OVER THE WEEKEND.

THE LAST ROUND OF S SWELL THAT MOVED NORTHWARD OVER EASTERN 
FORECAST WATERS THE PAST FEW DAYS IS BEGINNING TO SUBSIDE. A NEW 
SURGE OF CROSS-EQUATORIAL SWELL MOVING INTO THE AREA OVERNIGHT 
TONIGHT WILL BRING SEAS BACK TO 8 TO 10 FT IN EASTERN AND 
CENTRAL WATERS S OF 13N THROUGH SUN NIGHT.

$$
SCHAUER