000
AXPZ20 KNHC 162158
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC WED SEP 16 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2115 UTC.

...SPECIAL FEATURE...

TROPICAL STORM MARTY WAS LOCATED NEAR 18.9N 112.6W AT 21Z. 
MAXIMUM SUSTAINED WINDS WERE 40 KT WITH GUSTS TO 50 KT. MINIMUM 
CENTRAL PRESSURE WAS ESTIMATED AT 1001 MB. GOOD UPPER LEVEL 
ANTICYCLONIC OUTFLOW CONTINUES WELL ESTABLISHED OVER MARTY AND 
IS MAINTAINING A SMALL CDO CONVECTIVE PATTERN OVER THE SYSTEM. 
HOWEVER...THE UPPER HIGH ASSOCIATED WITH THIS FLOW HAS SHIFTED 
JUST FAR ENOUGH TO THE E TO PRODUCE MILD SE WIND SHEAR ACROSS 
MARTY...AND THIS IS MAINTAINING THE DEEP CONVECTION ON THE W 
SIDE OF THE CIRCULATION...PRODUCING AN ASYMMETRIC SYSTEM. THERE 
IS A VERY SHORT PERIOD THIS EVENING THROUGH THURSDAY FOR MARTY 
TO INTENSITY BEFORE ATMOSPHERIC AND OCEAN CONDITIONS BECOME LESS 
FAVORABLE. MARTY WAS ESTIMATED TO BE DRIFTING SLOWLY TOWARD THE 
NW TODAY...AND WILL LIKELY CONTINUE VERY SLOWLY TOWARD TO N OR 
N-NW DURING THE NEXT 12 TO 24 HOURS BEFORE INCREASING ITS 
FORWARD MOTION. MARTY IS SANDWICHED BETWEEN TWO DEEP LAYERED 
HIGHS...ONE TO THE E AND ANOTHER WELL TO THE W-NW...PREVENTING 
ANY SIGNIFICANT MOVEMENT OF THE SYSTEM. A MID TO UPPER LEVEL LOW 
AND TROUGH ALONG 120W AND OFFSHORE OF BAJA CALIFORNIA IS SINKING 
SLOWLY SOUTHWARD...AND HAS BEEN AIDING IN PRODUCING THE SOMEWHAT 
FAVORABLE ANTICYCLONIC OUTFLOW FOR MARTY. HOWEVER...AS THIS LOW 
SINKS FURTHER S AFTER 24 HOURS...SWLY INDUCED SHEAR IS EXPECTED 
TO COMBINE WITH COOLING SEA SURFACE TEMPS AND BEGIN A WEAKENING 
PROCESS FOR MARTY.

...TROPICAL WAVE...

A TROPICAL WAVE WAS ANALYZED ALONG 125W MOVING W 10 KT. THIS 
SMALL PERTURBATION HAS RECENTLY CAUGHT UP AND COME INTO PHASE 
WITH A WWD DRIFTING CONVERGENCE ZONE INDICATED IN SATELLITE AND 
TPW ANIMATIONS...ASSOCIATED WITH A LOW TO MID LEVEL LOW AND S 
EXTENDING TROUGH. THERE WAS ONLY ISOLATED CONVECTION WITHIN THE 
ITCZ ASSOCIATED WITH THIS WAVE.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE WAS ALONG THE LINE FROM 
09N84W TO 07N100W TO 12N118W TO 08N130W TO 09N140W. SCATTERED 
MODERATE WITHIN 120 NM S OF AXIS E OF 93W. SIMILAR CONVECTION IS 
NOTED WITHIN 80 TO 100 NM EITHER SIDE OF AXIS FROM 95W TO 105W. 
SCATTERED TO NUMEROUS MODERATE ISOLATED STRONG FROM 06N TO 10N W 
OF 137W. 

...DISCUSSION...

N OF 20N...A SURFACE RIDGE...ANCHORED ON A 1023 MB HIGH PRES 
NEAR 29N132W CONTINUES TO SLIDE SOUTHWARD OVER THE N WATERS. THE 
REGION IS MARKED BY MODERATE TO STRONG SUBSIDENCE 10-15 DEGREES 
W THROUGH NW OF MARTY...WITH BROKEN STRATOCUMULUS CLOUDS 
COVERING THE AREA N THROUGH NW OF MARTY AND THE ITCZ. THE PRES 
GRADIENT BETWEEN THIS RIDGE AND A SFC TROUGH OVER BAJA 
CALIFORNIA WAS PRODUCING NLY WINDS NEAR 20 KT AND SEAS NEAR 8 FT 
S OF 28N WITHIN 120 NM OF THE BAJA PENINSULA AND TO THE NW 
SEMICIRCLE OF MARTY. SATELLITE IMAGERY IS STILL SHOWING A WWD 
MOVING SWIRL OF LOW CLOUDS NEAR 23N144W ASSOCIATED WITH THE 
REMNANTS OF LINDA...WHICH IS REFLECTED AS A SURFACE TROUGH ON 
THE LATEST SURFACE MAPS. THE LEADING EDGE OF A COLD FRONT HAS 
STALLED ACROSS THE FAR NW CORNER OF THE AREA. A DEEP-LAYER 
TROUGH ACROSS THE FAR NE PACIFIC SUPPORTS THIS FRONTAL SYSTEM. 
THIS FRONT IS EXPECTED TO DISSIPATE E OF 130W THU...WHILE THE W 
PORTION IS FORCED SW. WAVE HEIGHTS WILL BUILD INTO THE 8 TO 10 
FT RANGE IN W-NW SWELL TONIGHT AND THU OVER THESE NW WATERS.

S OF 20N...ASIDE FROM TROPICAL STORM MARTY...THE TROPICAL 
WAVE...AND THE CONVECTION ALONG THE ITCZ...CONDITIONS ARE 
RELATIVELY QUIET OVER THE REMAINDER OF THE AREA. A DIFFLUENT 
PATTERN ALOFT OCCURRING ALONG THE SRN FLANKS OF THE TROPICAL 
UPPER RIDGE ALONG ABOUT 20N AND SPANNING THE FAR EPAC TO THE W 
CENTRAL CARIBBEAN IS HELPING TO VENTILATE AND SUSTAIN DEEP 
CONVECTION OVER THE EPAC WATERS AND ALONG THE ITCZ PARTICULARLY 
E OF 105W. 

WAVE HEIGHTS BETWEEN 105W AND 130W WERE GENERALLY RUNNING AT 8 
TO 9 FT IN A MIX OF LONG PERIOD NW SWELL AND SRN HEMI SE WIND 
SWELL. FRESH S TO SW FLOW ASSOCIATED WITH THE S AMERICAN MONSOON 
CIRCULATION WAS PRODUCING SEAS NEAR 8 FT ACROSS THE OPEN SEAS 
BETWEEN THE GALAPAGOS ISLANDS AND COSTA RICA. OTHERWISE...SEAS 
WERE GENERALLY LESS THAN 8 FT ACROSS THE AREA. NEW PULSES OF 
S-SW LONG PERIOD SWELL WILL MOVE INTO THE WATERS DURING THE NEXT 
FEW DAYS AND MIX WITH W AND NW SWELL...AND RAISE WAVE HEIGHTS 
ABOVE 8 FT E OF 110W...THU NIGHT THROUGH THE WEEKEND.

$$
STRIPLING