000
AXPZ20 KNHC 210935
TWDEP 

TROPICAL WEATHER DISCUSSION      
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT JUL 21 2007

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 
0845 UTC.

...TROPICAL WAVES...

TROPICAL WAVE 97W S OF 16N MOVING W 10 KT WITH A 1009 MB LOW 
ALONG THE AXIS NEAR 11N97W. CONVECTION HAS INCREASED AND A BAND 
HAS FORMED BUT IT DOES NOT APPEAR TO BE ASSOCIATED WITH THE LOW 
LEVEL CENTER. THE BAND IS W OF 100W WHILE THE LOW LEVEL CENTER 
IS NEAR 10N98W.  

TROPICAL WAVE ALONG 122W S OF 16N MOVING W 15 KT. THIS WAVE HAS 
BEEN DROPPED. THERE IS NO INDICATION OF IT. CONVECTION NEAR 
13N117W IS ASSOCIATED WITH A INVERTED MID LEVEL TROUGH THAT HAS 
BEEN IN THE AREA FOR A FEW DAYS.

...ITCZ...

ITCZ AXIS ALONG 9N77W 8N88W 10N99W 17N112W 8N130W 8N140W. 
SCATTERED MODERATE CONVECTION NEAR 8N79W 7N83W 9N97W 9N101W AND 
9N105W. SCATTERED MODERATE WITHIN 45 NM OF A LINE FROM 15N115W 
TO 8N127W TO 6N136W.

...DISCUSSION...

THERE REMAINS A WEAKNESS IN THE PRESSURE FIELD AT MID LEVELS 
BETWEEN 115W AND 135W. AN OLD UPPER TROUGH A FEW DAYS AGO WAS 
ACTIVE IN THIS AREA BUT HAS RECEDED NWD. AN INVERTED TROUGH FROM 
THE BAJA COAST SW REMAINS IN PLACE AND HAS BEEN DRIFTING NW. 
WATER VAPOR IMAGERY SHOWS A WEAK CYCLONIC CIRCULATION NEAR 
27N118W DRIFTING W. THIS CIRCULATION IS EMBEDDED IN THE INVERTED 
TROUGH. A WEAKER INVERTED MID LEVEL TROUGH IS ALONG 135W MOVING 
SLOWLY WWD. WATER VAPOR IMAGERY SHOWS A MOIST TONGUE EXTENDING N 
FROM THE ITCZ ON THE E SIDE OF THIS FEATURE. ON THE SURFACE 
TONIGHT A WEAK LOW HAS FORMED NEAR 10.5N98W ASSOCIATED WITH A 
TRPL WAVE AND IS MOVING W 10 KT. OTHERWISE THE PACIFIC RIDGE IS 
CENTERED NW OF THE AREA AND EXTENDS SE OT 20N120W. THE RIDGE IS 
PRODUCING NE TRADES TO 20 KT BETWEEN 10N AND 22N W OF 125W. 
WINDS ALONG THE BAJA COAST ARE MOSTLY LIGHT ACCORDING TO SSMI 
IMAGERY. GAP WINDS ARE ALSO LIGHT. CROSS EQUATORIAL SLY WINDS TO 
20 KT ARE EVIDENT IN SSMI S OF 10N BETWEEN 85W AND 105W AND 
BETWEEN 110W AND 130W.

LATER DAY 1 THE GFS MODEL SHOWS MID LEVEL RIDGING WORKING ACROSS 
THE AREA ALONG 30N TRYING TO FILL THE WEAKNESS. THE INVERTED 
TROUGH THAT HAS LINGERED OVER THE AREA WILL CONTINUE TO EXTEND 
FROM BAJA SW TO 15N130W BUT APPEARS TO BE TAKING A MORE WWD 
TRACK THAN LAST NIGHT MODEL WHICH SHOWED A NW MOTION. ON THE 
SURFACE LATER DAY 1 A WEAK PACIFIC RIDGE WILL CONTINUE OVER THE 
REGION N OF 10N W OF 120W WITH LITTLE CHANGE TO NE TRADES. WINDS 
ALONG BAJA WILL REMAIN LIGHT NWLY AS WILL GAP WINDS. CROSS 
EQUATORIAL SWELL TO 8 FT W OF 120W WITH SE WINDS TO 20 KT S OF 
10N. 

FOR DAY 2 GFS MODEL SHOWS UPPER TROUGH ALONG 140W N OF AREA 
GETTING NEW SURGE OF COLD AIR AND LOWERING MID LEVEL HEIGHTS 
SLOWLY OVER THE NW CORNER OF THE AREA. MID LEVEL RIDGING HOLDS 
FIRM OVER THE SW CONUS. THE INVERTED TROUGH OVER THE REGION FROM 
BAJA SW IS CAUGHT IN THIS RIDGE AND JUST CAN'T ESCAPE. THERE IS 
SOME INDICATION OF A SLIGHT NW DRIFT. ON THE SURFACE DAY 2 A 
1022 MB HIGH WILL ANCHOR THE PACIFIC RIDGE NEAR 28N135W BUT NE 
TRADES WILL REMAIN ABOUT THE SAME. WINDS ALONG BAJA WILL REMAIN 
LIGHT NWLY. GAP WINDS ALSO LIGHT. GFS MODEL SHOWS THE WEAK LOW 
MOVING TO NEAR 11N109W WITH LITTLE DEVELOPMENT. CROSS EQUATORIAL 
WINDS TO 20 KT MAINLY S OF 10N BETWEEN 100W AND 110W AND W OF 
120W.

$$
RRG