000 AXPZ20 KNHC 161513 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1505 UTC Mon Oct 16 2017 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 1200 UTC surface analysis and satellite imagery through 1400 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A gale has begun this morning over the Gulf region as high pressure is building over the eastern slopes of the Sierra Madre Mountains in Mexico and the western Gulf of Mexico in the wake of a cold front. Based off latest guidance, seas are currently peaking near 12 ft. Tonight, the combination of the forced gap winds and nocturnal influences will bring peak winds to just over 40 kt, which in turn will build seas reaching 13 to 15 ft during the overnight and early morning hours. Winds are forecast to diminish below gale force on Thursday, but the gap wind event will continue through the remainder of the forecast period, with northerly winds of 20 to 25 kt and seas to 8 ft Thursday through Friday night. Low pressure of 1007 mb is centered near 20N123W. Shower and thunderstorm activity remains concentrated to the east of the center of this system, with a cluster of moderate to strong convection from 18N to 24N between 118W and 123W. This system is forecast to move west- northwestward or northwestward into less conducive environmental conditions today, and the chance of this system becoming a tropical cyclone appears to be decreasing. There is currently a medium probability that this low will develop into a tropical cyclone within the next 48 hours. Please refer to the latest Tropical Weather Outlook for more information. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends across Central America near 09N82W to 09N99W, where it transitions to the ITCZ that continues to 08N113W to 11N121W. The ITCZ then resumes near 10N126W to 13N133W, then resumes W of low pres near 11N136W to beyond 09N140W. Scattered moderate and isolated strong convection are from 05N to 09N E of 80W, from 08N to 14N between 102W and 110W, and from 11N to 15N between 131W and 136W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see Special Features section above for information about the Gulf of Tehuantepec. A surface ridge extends across the waters off Baja California producing gentle to moderate winds and seas of 5 to 7 ft. The ridge will remain in place during the next few days with little change in winds and seas over the offshore waters aside from the Gulf of Tehuantepec region. By late Friday a weakening cold front and accompanying large NW swell event will spread over the waters W of Baja California. Broad high pressure over the central United States region is supporting moderate to fresh northwest winds over the northern and central Gulf of California, with seas nearing 4 to 5 ft. The high pressure will then shift eastward through Tuesday which will help to decrease winds over this area. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate to fresh offshore winds will develop across the Papagayo region each night through the middle of the week, with seas of 6 to 7 ft. Light and variable winds and seas of 4 to 6 ft in SW swell will prevail N of the monsoon trough, while gentle to moderate SW to W winds and seas of 5 to 7 ft in SW swell will prevail S of the trough. Swells originating from the gale in the Gulf of Tehuantepec will reach the offshore waters of Guatemala and El Salvador, building seas to 8 to 10 ft tonight through Wednesday. By Thursday, a fresh batch of SW swell will increase seas to 6 to 8 ft between Ecuador and the Galapagos Islands. REMAINDER OF THE AREA... Please see the Special Features section above for more information on low pressure centered near 20N123W. A 1006 mb low embedded in the ITCZ region near 12N135W is producing winds of 20 to 30 kt as indicated by an early morning scatterometer pass. This low will likely continue to generate strong winds and seas to 9 ft through tonight. Elsewhere, high pressure located N of Hawaii has a ridge axis that extends SE across the N waters to near 25N115W. Cross equatorial southwesterly swell will continue to propagate across the south- central waters, particularly S of 15N between 100W and 130W through late today, with seas of 8 to 9 ft. The aerial extent of the 8 ft seas or greater will diminish on Tuesday, and by Tuesday night, seas of 5 to 7 ft will dominate most of the waters W of 110W. Looking ahead...a cold front is forecast by the computer models to reach the far NW corner of the forecast region by Thursday night. A significant swell event will follow the front, with seas building to 10 to 16 ft over the NW waters by Friday, spreading across all the northern waters by Friday night. $$ Latto