000 AXPZ20 KNHC 190920 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Thu Oct 19 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A recent scatterometer pass provided observations of minimal gale force winds over the Gulf of Tehuantepec, with northerly winds of 20 to 30 kt extending downwind of the gulf to near 13N96W. Winds are forecast to diminish below gale force this morning, and seas will gradually subside during the day today. Winds of 20 to 30 kt and seas of 8 to 10 ft are expected during the overnight and early morning hours through early Saturday morning. In the Gulf of Tehuantepec, the first gale-force event of a season typically occurs in mid-October. The 10-year climatology indicates that on average 11.9 gale-force events and 6.3 storm- force events occur in the Gulf of Tehuantepec each cold season. About 84 percent of these events occur between November and March, with the largest number of gale-force winds ocurring in December. Storm-force events are most frequent in January. The next gale-force wind event is forecast by the computer models to occur in the Gulf of Tehuantepec Monday night into Tuesday as another cold front moves across the Gulf of Mexico. ...TROPICAL WAVES... A tropical wave is N of 04N along 85W moving W at 10 to 15 kt. Scattered moderate and isolated strong convection is noted within about 150 nm E of the wave axis. This convective activity is affecting parts of Honduras, Nicaragua and Costa Rica. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N85W to 08N100W to 10N120W. The intertropical convergence zone axis continues from 10N120W to 11N130W to 09N140W. Scattered moderate convection is from 07N to 09N between 91W and 105W. Isolated moderate convection is from 08N to 11N W of 110W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the Special Features section above for information about the ongoing Gulf of Tehuantepec gale event. A surface ridge extends SE into the waters off Baja California, producing mainly gentle to moderate NW to N 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 as described above. By Friday evening, a weakening cold front followed by a significant swell event will reach the waters W of Baja California Norte, causing winds to increase to 20 to 25 kt, with building seas between 8 and 12 ft across the waters N of 26N. Seas will continue to build to 14 to 16 ft in NW swell N of 27N Friday night. This swell event will continue propagating SE across the remaining offshore forecast waters W of Baja California, reaching the Revillagigedo Islands Saturday evening. High pressure in the wake of the front will dominate the northern forecast waters during the upcoming weekend. As a result, fresh to strong NW winds will persist over the offshore waters west off Baja California through early Saturday, with moderate to fresh NW winds prevaling thereafter. The pressure gradient between the high pressure and lower pressure in the vicinity of the Monsoon Trough/ITCZ will also bring mainly fresh trade winds across the west-central waters during the weekend. In addtion, expect fresh to strong N to NW winds across most of the Gulf of California by early Sunday morning, with seas building to 5 to 6 ft. These marine conditions are forecast to persist through Monday morning. 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 tonight, accompanied by seas of 5 to 7 ft. Otherwise, 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. Long period S to SW swell will reach the area between Ecuador and the Galapagos Islands this evening through Friday evening, building seas to 7 to 8 ft on Friday. REMAINDER OF THE AREA... Scatterometer data indicate that gentle to moderate winds dominate the northern forecast waters under the influence of a ridge being weakened by an approaching cold front. Seas continue to subside across most of the region W of 110W. An area of 8 ft seas primarily in SE swell is present across the SW corner, aminly S of 06N W of 131W. A new set of long period S to SW swell is forecast to cross the Equator today and propagate across the far southern waters, with resultant combined seas building back to 8 ft in the SW corner and far S central waters through Friday. The swell will then decay with seas subsiding to less than 8 ft during the upcoming weekend. A cold front is forecast to reach the far NW corner of the discussion area this evening while weakening. A significant swell event will follow the front as it weakens and dissipates while moving across the forecast waters N of 28N. Seas will build to 10 to 17 ft over the NW waters tonight and Friday. This swell event will continue to propagate SE covering the waters NW of a line from 30N115W to 24N113W to 11N140W by Friday night with seas of 8 to 15 ft. By Saturday night, the highest seas of 12 to 13 ft will dominate most of the waters N of 23N E of 125W, with seas of 8 to 12 ft affecting most of the area N of 05N W of 110W. Seas of 8 ft or greater will reach all the way to 110W on Sunday then continue to propagate SE, but begin to gradually decay thereafter through early next week. $$ GR