000 AXPZ20 KNHC 250952 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Sun Sep 25 2016 Tropical weather discussion for the eastern Pacific Ocean from the Equator to 32N, east of 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis. Based on 0600 UTC surface analysis and satellite imagery through 0945 UTC. ...SPECIAL FEATURES... A broad and elongated area of low pressure continues within the monsoon trough and is analyzed as 1006 mb low pressure near 14.5N120W. Scattered moderate isolated strong convection is observed within 120 nm either side of a line from 16N113W to 16N119W to 12N124W where banding features becoming more persistent. The pressure gradient is supporting strong winds within about 90 nm of the low center surrounded by fresh winds within 210 nm of the center, with seas of 8 to 12 ft. Atmospheric and oceanic conditions are favorable for tropical cyclone formation over the next several days. Even if it takes longer for the convection to organize into persistent bands, the pressure gradient is forecast to strengthen with minimal gale winds developing tonight over the ne quadrant of the low forecast near 16N119W. The low is forecast to move n reaching near 18N118W on Mon night with seas gradually building to about 18 ft. There is uncertainty in the intensity and track, please refer to the latest Graphical Tropical Weather Outlook for more information at http://hurricanes.gov. ...TROPICAL LOWS AND WAVES... A tropical wave is relocated to the n of 08N along 97W. Isolated moderate and strong convection is observed within about 150 nm either side of the wave axis. Expect the wave to gradually lose identity over the next few days. A 1009 mb low pressure is embedded in the monsoon trough near 12N137W. Scattered moderate isolated strong convection is noted within 45 nm either side of a line from 12N134W to 14N137W to 12N139W, but currently lacks persistent banding. The low is forecast to move w to near 12N140W late tonight, then stall and strengthen on Mon and Tue, then move ne and back into the area near 15N140W on Wed night accompanied by at least strong winds. Atmospheric and oceanic conditions will become more favorable for tropical cyclone formation in 3 to 5 days. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends w off the Pacific coast of northern Costa Rica at 10N85W to 10N96w, then dips sw to 08N110W where it loses identity. Scatterometer winds indicate that the monsoon trough resumes just sw of the surface low at 14.5N120W, and continues sw to 11N127W, then turns nw through the 1009 mb surface low at 12N137W, and continues w to beyond 12N140W. Scattered moderate isolated strong convection is observed within 120 nm either side of a line from 04N77W to 08N82W, and within 30 nm either side of a line from 11N124W to 13N133W. Isolated moderate and strong convection is noted elsewhere n of 05N between 82W and 107W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A sub-tropical ridge axis extends from nw to se across the offshore zones w of the Baja Peninsula terminating near 22N112W. Gentle nw winds are observed w of the Baja Peninsula with little change expected through Mon night, then the gradient should relax supporting light n winds through early Wed. Gentle to occasionally moderate flow expected elsewhere along the Pacific coast of Mexico today. Uncertainty begins tonight as the tropical low previously described, moves northward and begins to affect the w portion of offshore PMZ015, with gale conditions forecast in that area on Tue and shifting n across the far outer portion of PMZ013 on Wed night. Plenty of uncertainty, so expect fluctuations in track and intensity forecasts for the next few days. Fresh to occasionally strong nw winds are expected across the northern Gulf of California through Mon morning, then the gradient will relax supporting mostly moderate n flow through Tue. Gentle to moderate n flow expected across the gulf waters elsewhere n of 25N today, then light the gentle n flow beginning on Mon night. Light and variable winds forecast s of 25N this week. Guidance is hinting at a fairly strong cold front reaching the sw Gulf of Mexico on Tue, resulting in strong drainage flow across the Gulf of Tehuantepec beginning late Wed, and increasing to near gale force late Wed night, and continuing through Thu, with minimal gale conditions on Thu night. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Light to gentle southerly winds expected n of about 08N, while gentle to locally moderate s to sw flow is expected s of 08N through the middle of the week. Combined seas of 3 to 6 ft primarily in mixing long-period sw and nw swell are expected through the middle of the week. REMAINDER OF THE AREA... The pressure gradient between the low previously described near 12N137W and the subtropical ridge to the n, will maintain fresh ne trades, and combined seas of 6 to 9 ft, across the discussion waters roughly from 13N to 23N between 130W and 140W today, with these conditions gradually diminishing/subsiding from the ne to 20 kt or less, and seas less than 8 ft early Mon. $$ Nelson