000 AXPZ20 KNHC 180930 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 601 UTC Wed Oct 18 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: Gale force winds are blowing across the Tehuantepec area. Salinas Cruz, Mexico is reporting sustained N winds of 25 kt. This gap wind event is the result of a tight pressure gradient between high pressure across the eastern slopes of the Sierra Madre Mountains in Mexico, and across the western Gulf of Mexico in the wake of a stationary front which extends from N to S over the central Bay of Campeche. Seas are in the range of 10 to 15 ft across the area of gale force winds, with seas of 8 ft or greater spilling out to areas downwind of the gale. Global model guidance indicates that the high pressure will weaken through Thursday, with the corresponding tight gradient slackening. This will allow for the gale force winds to eventually diminish to below gale force just after sunrise on Thursday, however, northerly winds of 20 to 30 kt will continue through Friday along with seas of 8 to 10 ft. Looking ahead, another gale force wind event is possible early next week. ...TROPICAL WAVES... A tropical wave is N of 06N along 83W, moving W at 10 to 15 kt. A cluster of moderate to isolated strong convection is along the wave axis near 13N. This convective activity is currently affecting Nicaragua. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends across parts of Panama and Costa Rica near 10N86W to 08N100W to 09N110W. The intertropical convergence zone axis continues from 09N110W to 10N120W to 07N135W to beyond 09N140W. Scattered moderate to strong convection is noted along the coast of Colombia N of 03N, and in the Gulf of Panama N of 07N. Scattered moderate isolated strong convection is from 08N to 11N between 94W and 100W, and from 08N to 11N between 110W and 130W. ...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 across 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 afternoon into Friday evening a weakening cold front and accompanying set of large NW swell will propagate through the waters W of Baja California building seas to 8 to 12 ft across the waters N of 27N. Seas will continue to build to 14-15 ft in NW swell by Friday night. This swell event will continue to propagate across the offshore forecast waters on Saturday. Also on Friday, expect increasing winds of 20to 25 kt over the waters adjacent to Baja California Norte as high pressure in the wake of the front begins to dominate the northern forecast waters. Mainly gentle to moderate NW to N winds are expected over most of the Gulf of California through early Wednesday, then winds become light and variable through Friday. Seas will be mainly 2 ft or less, except for higher seas of 3 to 5 ft at the entrance to the gulf in SW swell subsiding to 3 to 4 ft Wednesday through Thursday night, and then to 2 to 3 ft on Friday. Seas will build back to 3 to 5 ft near the entrance during the upcoming weekend as southerly swell reaches 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 Thursday night, with seas of 5 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 force wind event in the Gulf of Tehuantepec will reach the far western section of the offshore waters of Guatemala and El Salvador, building seas to 8 to 10 ft there through this afternoon, subsiding to 6 to 8 ft this evening, and to 5 to 6 ft on Thursday. Long period SW swell is forecast to reach the area between Ecuador and the Galapagos Islands from Thursday evening into Friday, building seas to 7 to 8 ft on Friday. REMAINDER OF THE AREA... The low pressure area previously located near 24N128W has weakened, and a surface trough is analyzed on the 0600 UTC surface map extending from 22N128W to 27N128.5W. Winds and seas have diminished in association with this feature. The low pressure area located over the west-central waters near 16N140W has also weakened and now a trough is analyzed west of the forecast region. Seas of 8 to 9 ft in mixed NE and NW swell are still noted over the forecast waters in association with this trough from 15N to 21N W of 136W. A pair of altimeter passes confirmed the presence of these sea heights. Elsewhere, gentle to moderate winds are noted across the northern forecast waters under the influence of a weak ridge. Seas continue to subside across most of the region W of 110W with an area of 8 ft seas in mixed swell S of 05N W of 130W. A new set of long period southerly swell is forecast to cross the Equator on Thursday and propagate across the far southern waters with resultant combined seas building back to 8 to 9 ft in the SW corner and far S central waters through Friday before decaying during the upcoming weekend. Looking ahead, a cold front is forecast by the global 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 Thursday night into early Friday before spreading across all the northern waters W of 115W, and across the west-central waters by late Friday night. Seas of 8 ft or greater will reach all the way to 110W by early Sunday then will begin to gradually decay while reaching to 100W thereafter. $$ GR