000
AXPZ20 KNHC 171021
TWDEP 

TROPICAL WEATHER DISCUSSION    
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC TUE MAR 17 2009

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 
0945 UTC.

...ITCZ...

THE ITCZ AXIS WAS ALONG A LINE FROM 06N77W TO 05.5N85W TO 
04N100W THEN DIFFUSE TO 04N120W THEN CONTINUING TO 08N140W. 
ISOLATED WEAK CONVECTION WAS ALONG THE ITCZ E OF 122W. SCATTERED 
MODERATE CONVECTION WAS WITHIN 60 NM S AND 90 NM N OF AXIS W OF 
135W.

...DISCUSSION...

THE DEEP LAYER LOW N OF HAWAII HAS MOVED E-SE DURING THE PAST 8 
HOURS AND APPEARS MORE WELL DEFINED IN WATER VAPOR IMAGERY. THIS 
LOW IS FORECAST TO GRADUALLY WEAKEN AND MOVE MORE E-NE OVER THE 
NEXT FEW DAYS...AND ACT TO TEMPORARILY SHIFT THE SUBTROPICAL 
RIDGE OVER N CENTRAL WATERS FARTHER NORTHWARD.  THIS LOW IS 
EXPECTED TO PHASE WITH THE NORTHERN STREAM TROUGH CURRENTLY 
APPROACHING IT FROM THE NW...AND MOVE EASTWARD THROUGH THE N 
WATERS.  TROUGHING AT LOW LEVELS ASSOCIATED WITH THIS LOW WILL 
WILL MAINTAIN A MEAN TROUGH OR FRONTAL BOUNDARY OVER THE NW 
WATERS THROUGH THU. NW SWELL ASSOCIATED WITH A STRONG MID 
LATITUDE SYSTEM FARTHER N HAS BEGUN TO INVADE NW PORTIONS OF THE 
AREA OVERNIGHT...AND WILL BUILD DURING THE NEXT 24 HOURS.

THE DEEP LAYER TROUGH CURRENTLY DRAGGING ACROSS THE NRN GULF OF 
MEXICO WILL PULL SLOWLY EASTWARD OVER THE NEXT DAY OR TWO...AND 
CARRY THE ASSOCIATED SURFACE COLD FRONT EASTWARD THROUGH THE 
SOUTHWEST GULF OF MEXICO...AND GRADUALLY SLACKEN THE PRESSURE 
GRADIENT OFF THE W CENTRAL COAST OF BAJA CALIFORNIA BETWEEN THIS 
TROUGH AND THE SUBTROPICAL PACIFIC HIGH. WINDS OFF OF THE BAJA 
HAVE BEEN BLOWING AS HIGH AS 25 KT FOR THE PAST 24 HOURS...WITH 
NEAR 20 KT FLOW CURRENTLY ACROSS THE SRN GULF OF CALIFORNIA. AT 
THE SAME TIME...STRONG NORTHERLY FLOW BLEEDING THROUGH THE 
ISTHMUS OF TEHUANTEPEC HAS INCREASED TO NEAR GALE FORCE 
OVERNIGHT...AND IS EXPECTED TO LAST THROUGH WED MORNING. RECENT 
MODEL GUIDANCE HAS SUGGESTED TWO SEPARATE PULSES OF GALES... 
SUGGESTING THAT WINDS MAY PEAK LATE THIS MORNING...THEN POSSIBLY 
DROP BELOW GALE FORCE LATE THIS AFTERNOON/EARLY EVENING...AND 
THEN RETURN TO GALE FORCE TONIGHT THROUGH WED MORNING.

WINDS SHOULD CONTINUE TO PULSE UP AND DOWN BUT REMAIN AT OR 
ABOVE 20 KT THROUGH THE FORECAST PERIOD ACROSS AND DOWNWIND A 
SHORT DISTANCE OF THE GULF OF PAPAGAYO...AS STRONG TRADE WINDS 
MOVE THROUGH CENTRAL AMERICA.  THE HIGH PRESSURE RIDGE ACROSS 
THE EASTERN GULF OF MEXICO HAS BEGUN TO SHIFT SOUTHWARD INTO THE 
NW CARIBBEAN AS THE COLD FRONT OVER THE NORTHERN GULF HAS BEEN 
DRAGGED EASTWARD. THIS WILL ALLOW THE PRESSURE GRADIENT TO  
BUILD BETWEEN THIS RIDGE AND THE CLIMATOLOGICAL LOW PRESSURE 
OVER NORTHERN COLOMBIA...AND AID IN ENHANCING GAP FLOW FROM THE 
SOUTHWEST CARIBBEAN ACROSS CENTRAL AMERICA THROUGH THE FORECAST 
PERIOD. THIS IS ALSO EXPECTED TO MAINTAIN A 20 KT FLOW DOWNWIND 
OF THE GULF OF PANAMA...WITH LITTLE CHANGE EXPECTED THERE ALSO 
OVER THE NEXT TWO DAYS.

A BROAD ZONE OF 20-25 KT NE TO E WINDS INDUCED BY THE 
SUBTROPICAL RIDGE WAS YIELDING A CONVERGENCE LINE AND SCATTERED 
MODERATE CONVECTION ACROSS W PORTIONS OF THE FORECAST 
AREA...ALONG ABOUT 10N...WHERE DEEPEST MOISTURE CONTINUES TO 
RESIDE. NORTH OF THIS CONVERGENCE ZONE...AND WITHIN THIS BROAD 
E-NE WIND FETCH...SEAS OF 8 TO 11 FT PERSIST IN A CONFUSED MIX 
OF MERGING NW AND SW LONG PERIOD SWELL...AND NE WIND WAVES. WAVE 
HEIGHTS THERE WILL SLOWLY SUBSIDE OVER THE NEXT 48 HOURS AS THE 
SW SWELL FADES AND THE NW SWELL BECOMES DOMINANT.

OTHERWISE...LITTLE CONVECTION WAS OCCURRING OVER THE FORECAST 
AREA OVERNIGHT. WIDESPREAD SUBSIDENCE DOMINATING MOST OF THE 
TROPICAL EPAC E OF 115W FOR THE PAST FEW DAYS HAS ABATED...BUT 
THE LOW AND MIDDLE ATMOSPHERE THERE GENERALLY REMAIN STABLE AND 
DRY...AND ARE INHIBITING CONVECTION IN THAT AREA. 

$$
STRIPLING