000
AXPZ20 KNHC 200318
TWDEP 

TROPICAL WEATHER DISCUSSION     
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC FRI MAR 20 2009

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 
0230 UTC.

...ITCZ...
THE ITCZ AXIS LIES ALONG A LINE FROM 08N83W TO 05N93W TO 04N106W 
04N120W TO 03N131W TO 03N140W. NO SIGNIFICANT CONVECTION 
IS NOTED ALONG THE ITCZ.

...DISCUSSION...

THE UPPER LEVEL FLOW CONTINUES TO AMPLIFY N OF THE DISCUSSION 
AREA AS AN UPPER LEVEL JET MAXIMUM DIVES SOUTHWARD...FORCING AN 
UPPER TROUGH TO DIG SOUTHWARD. A COLD FRONT N OF THE AREA 
CONTINUES ADVANCING SOUTHWARD...AND IS FORECAST TO ENTER THE 
NORTHERN WATERS BY SUNDAY. NW TO N WINDS OF 20 TO 30 KT WILL 
AFFECT AREAS IN THE WAKE OF THE FRONT...WHERE WAVE HEIGHTS OVER 
14 FT IN NORTHWESTERLY SWELL WILL BE PRESENT. GALES ARE EXPECTED 
TO REMAIN N OF THE AREA...WHERE THE STRONGER SURFACE PRESSURE 
GRADIENT WILL BE LOCATED.

IN THE MEANTIME...A 1024 MB SURFACE HIGH N OF THE AREA NEAR 
32N136W WILL DISSIPATE DURING THE NEXT DAY IN RESPONSE TO 
DECREASING DEEP LAYER SUBSIDENCE WITH THE AMPLIFICATION OF THE 
UPPER TROUGH. WAVE HEIGHTS UP TO 9 FT IN NORTHWESTERLY SWELL 
CONTINUE IN NORTH CENTRAL PORTIONS OF THE DISCUSSION AREA...BUT 
CONTINUE SUBSIDING AS THEY DEPART THEIR SOURCE REGION AND WINDS 
DIMINISH. THE ENHANCED SURFACE PRESSURE GRADIENT AT THE SOUTHERN 
PERIPHERY OF THE SURFACE HIGH ALSO IS ENHANCING NE TO E TRADES 
ACROSS THE REGION. THE QUIKSCAT PASS AROUND 20/0200 UTC SHOWED 
NE TO E WINDS UP TO 20 KT FROM 05N TO 18N W OF 120W...WITH 
WAVEWATCH GUIDANCE INDICATING SEAS TO 9 FT IN THIS AREA WITH 
CONTINUING NE SWELL. THE TRADES IN THIS AREA ARE EXPECTED TO 
PICK UP SUBSTANTIALLY ON SUNDAY AS A SURFACE HIGH BUILDS 
SOUTHWARD IN THE WAKE OF THE AFOREMENTIONED COLD FRONT.

AS FOR CONVECTIVE ACTIVITY...UPPER LEVEL DIFFLUENCE N OF THE 
ITCZ AXIS IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 16N 
TO 22N W OF 123W. FARTHER TO THE E...DEEP LAYER DRY AIR AND 
STABLE ATMOSPHERIC CONDITIONS EMBEDDED WITHIN AN UPPER RIDGE ARE 
RESULTING IN FAIR WEATHER CONDITIONS S OF 16N E OF 100W.

GAP WINDS...
A PERSISTENT RIDGE OF SURFACE HIGH PRESSURE OVER MEXICO AND THE 
GULF OF MEXICO WILL SUPPORT A RELATIVELY STRONG SURFACE PRESSURE 
GRADIENT ACROSS THE ISTHMUS OF TEHUANTEPEC DURING THE NEXT FEW 
DAYS. CORRESPONDINGLY...THE HIGH RESOLUTION ASCAT PASS AROUND 
20/0020 UTC DEPICTED N TO NE WINDS OF 20 TO 25 KT FUNNELING INTO 
THE GULF OF TEHUANTEPEC. STRONG SURFACE HIGH PRESSURE BUILDING 
SOUTHEASTWARD FROM SW ONTARIO CANADA WILL STEEPEN THE PRESSURE 
GRADIENT ACROSS THE ISTHMUS OF TEHUANTEPEC EVEN FURTHER ON 
FRIDAY...WHEN WINDS WILL INCREASE ACROSS A LARGER AREA IN THE 
GULF OF TEHUANTEPEC. COMPUTER MODEL GUIDANCE IS TRENDING UPWARD 
WITH THE INTENSITY OF THESE WINDS DESPITE THE ABSENCE OF ANY 
SUBSTANTIAL SURFACE FRONTS. IN FACT...GALE FORCE WINDS ARE 
EXPECTED FROM LATE TONIGHT THROUGH SATURDAY MORNING IN THE GULF 
OF TEHUANTEPEC...GIVEN THE STRONG PRESSURE GRADIENT SW OF A 1035 
MB SURFACE HIGH OVER THE MID ATLANTIC STATES THIS WEEKEND. SEAS 
WILL BUILD OVER 10 FT DOWNWIND OF THE GULF OF TEHUANTEPEC BY 
SATURDAY. ALSO...TRADE WINDS ACROSS THE CARIBBEAN CONTINUE WITH 
A PERSISTENT SURFACE LOW OVER NW COLOMBIA. THESE WINDS CONTINUE 
TO BLEED INTO THE GULF OF PAPAGAYO. GAP WINDS AROUND THE GULFS 
OF TEHUANTEPEC AND PAPAGAYO ARE FORECAST TO BE STRONGEST LATE AT 
NIGHT WHEN DRAINAGE FLOW OFF HIGHER TERRAIN IS MAXIMIZED IN THE 
PRESENCE OF DEEP LAYER DRY AIR.

$$

COHEN