000 AXPZ20 KNHC 170846 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: October marks the beginning of the Tehuantepec wind events. The first gale-force event of a season typically occurs in mid- October. Currently, gale force winds of 30 to 35 kt are noted across the Tehuantepec area based on a recent ASCAT pass. Building 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 cold front, located over the central Bay of Campeche, supports this gap wind event. Winds are forecast to further increase to 40 kt early this morning with seas building to 14-15 ft. Gale force winds are expected to persist across the Tehuantepec region through Wednesday night. Then, 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 30 kt and seas of 8 to 10 ft Thursday through early Friday morning. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends across Panama and Costa Rica to near 09N85W to 08N95W to 08N102W. The ITCZ continues from 08N102W to 09N108W to 08N120W to 11N130W to low pressure 1007 mb near 14N136W to 11N140W. Scattered moderate convection is noted from 08N to 10N between 95W and 103W. Scattered moderate isolated strong convection is within about 180 nm N of ITCZ axis between 111W and 118W. Similar convection is near 11N136W. ...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 building seas to 12-14 ft. Winds have diminished below 20 kt over the northern and central Gulf of California as high pressure, previously located over the Great Basin, moves eastward. A recent ASCAT pass indicates mainly moderate NW winds over this area. Expect mainly gentle to moderate NW-N winds across most of the Gulf of California through Wednesday, with light and variable winds on Thursday. 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 Thu night, 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 force wind event in the Gulf of Tehuantepec will reach the offshore waters of Guatemala and El Salvador, building seas to 8 to 10 ft today through Wednesday. Long period SW swells are forecast to reach the area between Ecuador and the Galapagos Islands late Thu into Fri, building seas to 7 to 8 ft on Fri. REMAINDER OF THE AREA... A low pressure near 22N126W has weakened. 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 120 NM in the NE semicircle of the low with seas of 8-10 ft based on altimeter data. This low will degenerate into a trough late tonight into Wednesday. A 1007 mb low pressure embedded in the ITCZ region near 14N136W is producing winds of 20 to 25 kt with seas of 8 to 9 ft based on altimeter data. This low will also open up into a trough by tonight as it moves westward, reaching near 140W. 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 south-central waters, and currently seas of 8-9 ft are noted mainly S of 10N between 105W and 135W. By tonight, seas of 5 to 7 ft will dominate much 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 W of 115W, and across the west-central waters by late Friday night. $$ GR