000 AXPZ20 KNHC 191602 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1501 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 1200 UTC surface analysis and satellite imagery through 1430 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: High pressure along the Sierra Madre Oriental of Mexico is weakening, which is allowing the pressure gradient over the isthmus of Tehuantepec to relax. Winds are still expected to diminish below gale force over the Gulf of Tehuantepec by mid afternoon today. Seas in this area will gradually subside as well. Winds of 20 to 30 kt and seas of 8 to 10 ft are then expected during the overnight and early morning hours through early Saturday morning. Strong gap winds from Sat through Sun will occur during the nocturnal drainage maximum and be restricted to N of 15N until late Sun night, when winds over the Gulf of Tehuantepec will ramp up again in response to the next cold front entering the Gulf of Mexico. ...TROPICAL WAVES... A tropical wave is N of 03N along 86W moving slowly W around 5 kt. Scattered moderate and isolated strong convection is noted from 05N to 10N between 82W and 88W. This convection is situated just SW of the coasts of Panama and Costa Rica. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 09N84W to 08N103W to 09N110W to 10N120W. The intertropical convergence zone axis continues from 10N120W to 11N127W to beyond 09N140W. Scattered moderate and isolated strong convection is present within 60 nm either side of a line from 10.5N123W to 12.5N129W to 12.5N133W. Scattered moderate convection is seen from 06N to 10N between 94W and 107W and from 07N to 10N between 122W and 124W. ...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 weakening 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 along the Pacific coast of Baja. A weakening cold front will reach 30N140W late tonight. By Friday evening, the front will have lost identity near Baja but will usher in a significant swell event from Fri evening through Mon. High pressure building in behind the front will cause winds to increase to 20 to 25 kt, with building seas between 8 and 12 ft across the waters N of 26N during the day on Fri. 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 prevailing 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 addition, expect fresh to strong N to NW winds to commence across the Gulf of California by dawn on Sunday, the spread SE over the remainder of the Gulf Sun night and Mon with seas peaking at 5 to 6 ft. Winds will subside below advisory levels by Mon evening, but reinforcing NW swell will maintain seas above 8 ft W of Baja through the middle of next week. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate to fresh offshore winds will develop nightly across the Papagayo region through Sat night, 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 reaching the area between Ecuador and the Galapagos Islands will maintain seas around 8 ft this evening through Friday evening. Moderate to fresh SW winds will cause seas to build to around 8 ft W of Colombia and S of Panama between 03N and 06N between 80W and 84W. REMAINDER OF THE AREA... 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, mainly S of 04N and W of 135W. 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 near the SW corner of the discussion area and in the waters near the Equator to the W of the Galapagos Islands through Friday night. The swell will then decay with seas subsiding to less than 8 ft this weekend. A cold front will reach the far NW corner of the discussion area this evening as it weakens. However, the large fetch of gales that has been in place to the NW of the front has already generated large long period swell which are propagating SE. Consequently, a significant swell event is expected. Seas will build to 10 to 16 ft over the NW waters tonight and Friday. The swells will continue to propagate SE to bring 8 ft seas to the waters NW of a line from 27N115W to 14N140W by Friday night. Seas will be highest at around 15 ft near 30N 130W. By Saturday night, the highest seas of 12 to 13 ft will dominate most of the waters N of 23N E of 125W. Seas of 8 to 12 ft will affect most of the area N of 08N 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. $$ CAM