000 AXPZ20 KNHC 180221 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0221 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 0215 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Gale force winds are present across the Tehuantepec area as clearly depicted by an earlier ASCAT scatterometer passes. These gale force winds are supported by 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 04N along 82W continuing northward along the Costa Rica/Panama border and offshore of the Caribbean coast of Nicaragua in the SW Caribbean Sea, moving W at 10 to 15 kt. Associated convection has diminished during the past several hours. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N74W to 10N90W to 11N114W to low pressure near 10N118W to 10N120W. The intertropical convergence zone axis extends from 10N120W to 08N126W to 11N140W. Scattered moderate and isolated strong convection is from 07N to 11N between 92W and 95W, from 07N to 10N between 105W and 111W, and within an area bounded by 13N122W to 13N118W to 07N114W to 07N128W to 13N122W. ...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, with the pressure gradient between it and troughing along the eastern part of Baja California bringing 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 late 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 the 8 to 15 ft range. Also on Friday evening, NW winds will increase to fresh over the waters adjacent to Baja California Norte. 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. 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 today through Wednesday, subsiding to 6 to 8 ft Wednesday evening and to 5 to 6 ft 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 6 to 8 ft on Friday. REMAINDER OF THE AREA... Low pressure of 1013 mb near 24N128W continues to rapidly weaken under very strong W to SW upper winds. Latest satellite imagery shows the low level center exposed and elongated with no deep convection present. Winds are 20 kt or less with the low, however, some residual seas to 8 ft in mixed swell persist within 150 nm in the N quadrant of the low as sampled by recent altimeter passes. This low will dissipate into a trough by late tonight with associated seas subsiding to less than 8 ft by then. A 1009 mb low pressure area is over the W central waters near 16N140W. Associated winds are moderate to fresh with some seas to 8 ft mainly NW swell on the E side of the low. This feature will move W of 140W through tonight with associated conditions E of 140W subsiding t less than 8 ft by early Wednesday. Elsewhere, gentle to moderate winds are noted across the northern forecast waters under the influence of a weak ridge. Seas continue to subside across the S central waters, with an area of 8 to 9 ft seas in mixed swell. The mixed swell is forecast to gradually decay through the end of the week, however a new batch of SW swell is forecast by Wave model guidance to propagate through the far southern waters beginning on Thursday 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. $$ Lewitsky