000 AXPZ20 KNHC 170245 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 207 UTC Tue Oct 17 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 0000 UTC surface analysis and satellite imagery through 0230 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: An earlier 1550 UTC ASCAT pass indicated an area of 30 to 35 KT gale force winds within 90 nm of the coast of Mexico from 20N to 25N 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 strong cold front. Recent surface observations at Minatitlan indicated strong northerly winds up to 30 KT suggesting a gap wind event is in progress in the Gulf of Tehuantepec. Gridded forecast data suggests winds have already reached gale force. The event is forecast to peak in intensity later tonight through most of Tuesday with winds possibly reaching 40 to 45 KT and seas peaking at 10 to 15 FT. Winds are forecast to diminish below gale force early 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. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends across Central America near 09N85W to 08N92W, then transitions to the ITCZ near 09N105W and continues to 09N115W to 13N130W to low pressure 1007 mb near 13N137W. Scattered moderate and isolated strong convection was noted from 08N to 11N between 108W and 117W. Scattered moderate convection was noted from 11N to 15N between 134W and 137W. ...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. An earlier 1732 UTC ASCAT pass confirmed 20 KT winds over the Gulf of California from 25N to 28N. The high pressure will then shift eastward through Tuesday which will help to decrease winds over the 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... Low pressure near 22N125W has weakened and is no longer in the Special Features section. Convection has become less organized and is being sheared away from the low level center. Winds of 20 to 25 kt are estimated to be occurring within 150 NM in the N semicircle of the low. A 1007 mb low embedded in the ITCZ region near 13N137W is producing winds of 20 to 25 kt as indicated by the edge of an afternoon scatterometer pass. This low will likely continue to generate fresh winds and seas to 9 ft through tonight. the low will degenerate into atrough on Thu with winds and seas subsiding below High Seas criteria. Elsewhere, 1029 MB 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 aereal 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 NWP 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 17 ft over the NW waters by early Friday, spreading across all the northern waters by late Friday night. $$ Cobb