000
AXPZ20 KNHC 180917
TWDEP 

TROPICAL WEATHER DISCUSSION    
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI MAY 18 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.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N77W 11N90W 8N100W 9N111W 10N129W 
7N140W. ISOLATED MODERATE TO STRONG CONVECTION NEAR 5N78W 7N82W 
7N87W 9N88W 11N88W 13N89W 8N92W 10N94W 8N96W 8N98W AND 7N104W. 
SCATTERED MODERATE TO STRONG CONVECTION WITHIN 45 NM EITHER SIDE 
OF A LINE FROM 7N112W TO 9N125W TO 6N139W.

...DISCUSSION...

A MODERATE SRN BRANCH OF THE WESTERLIES CONTINUES TONIGHT 
HEADING ENE ACROSS BAJA AND NRN MEXICO. A LARGE FLAT MID LEVEL 
RIDGE COVERS THE S OF 20N STILL BULGING NWD OVER MEXICO ALONG 
105W. A MODERATE SHORTWAVE TROUGH WAS ALONG 120W MOVING SLOWLY 
ENE BUTTING UP AGAINST THE BULGING RIDGE. A LARGE AREA OF VERY 
DRY MID AND UPPER ATMOS AIR LIES AHEAD OF THIS SHORTWAVE 
PROBABLY A RESULT OF THE BULGING RIDGE AND NOT THE TROUGH. 
STRONG UPPER TROUGH LIES NW OF THE REGION AND IS EMBEDDED IN THE 
NRN BRANCH OF THE WESTERLIES. ON THE SURFACE TONIGHT BRIEF GALE 
CONDITION THROUGH TEHUANTEPEC EARLIER TODAY HAS DIMINISHED 
TONIGHT AND THE GALE WILL BE DISCONTINUED. SSMI SHOWS ONLY 15 TO 
20KT. A 1025 MB HIGH CENTER OF THE PACIFIC RIDGE IS NEAR 29N133W 
AND IS RESPONSIBLE FOR NE TRADES 20 TO 25 KT S OF 20N W OF 125W 
AND ALSO NW WINDS 20 TO 25 KT N OF 27N BETWEEN 118W AND 122W. 

LATER DAY 1 THE SHORTWAVE OFF THE BAJA COAST MAKES LITTLE 
PROGRESS ENE BUT DOES APPEAR TO INTERACT WITH THE NRN BRANCH 
MORE ACCORDING TO THE GFS MODEL. THIS MAY BE IT'S ONLY HOPE OF 
DEALING WITH THE PERSISTENT RIDGE WHICH LIES OVER NRN MEXICO AND 
THE SW CONUS. ON THE SURFACE LATER DAY 1 LITTLE CHANGE TO THE 
PACIFIC RIDGE WITH A 1026 MB CENTER NEARLY STATIONARY NEAR 
29N132W. GAP WINDS MOSTLY LIGHT EXCEPT FOR TEHUANTEPEC WHERE N 
TO NE WINDS OF 20 KT CAN BE EXPECTED. THE GFS MODEL CONTINUE TO 
SHOW A INCREASE IN SW WINDS S OF 8N E OF 88W WITH SEAS TO 8 FT. 
THE MODEL PICKS UP ON SLOWLY FALLING PRES OVER SW CARIB WHICH 
MAY ACCOUNT FOR THE SLIGHT INCREASE IN WINDS.

FOR DAY 2 WHILE THE SHORTWAVE OFF THE BAJA COAST MAKES LITTLE 
PROGRESS ENE..IT APPEARS TO BE INTERACTING WITH THE NRN BRANCH 
MORE AND MORE WITH TIME..GAINING MORE STRENGTH. THE RIDGE OUT 
AHEAD OF THE SHORTWAVE ALSO STRENGTHENS WHICH MAINTAINS THE 
STATUS QUO. OPEN MID LEVEL RIDGING BEGINS DEVELOPING ALONG 135W 
IN RESPONSE TO WEAKENING OF THE LARGE UPPER TROUGH TO THE N AND 
NW. ON THE SURFACE DAY 2 A 1028 MB HIGH CENTER OF THE PACIFIC 
RIDGE MEANDERS BACK TO NEAR 30N135W MAINTAINING NE TRADES TO 25 
KT S OF 10N W OF 125W AND NW WINDS OF 20 KT BETWEEN 118W AND 
124W. LITTLE CHANGE ELSEWHERE..SOME MODERATE N TO NE WINDS 
CONTINUE THROUGH TEHUANTEPEC WHILE OTHER GAP AREAS REMAIN LIGHT. 
WINDS SW OF PANAMA REMAIN 15 TO 20 KT WITH S SWELL TO 8 FT. 

$$
RRG