000 AXPZ20 KNHC 160922 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Mon Oct 16 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 provides observations of northerly winds in the 20-30 kt range over the Gulf of Tehuantepec. Winds are forecast to further increase to minimal gale force early this morning as high pressure builds over the eastern slopes of the Sierra Madre Mountains in Mexico and the western Gulf of Mexico in the wake of a cold front moving across the region. Seas will reach 13-15 ft during the overnight and early morning hours when winds will peak near 40 kt. Winds are forecast to diminish below gale force on Thursday, but the gap wind event will continue through the remainder of the forecast period. By Friday night, expect northerly winds of 20-25 kt and seas to 8 ft. A low pressure of 1006 mb is centered near 19N122W. Shower and thunderstorm activity associated with this feature has changed little over the past several hours. Satellite imagery shows that a band of numerous moderate convection persists mainly NE of the low center, covering the waters from 18N to 21N between 120W AND 122W. This system is forecast to move west-northwestward or northwestward into less conducive environmental conditions today, and the chance of this system becoming a tropical cyclone appears to be decreasing. There is currently a medium probability that this low will develop into a tropical cyclone within the next 48 hours. Please refer to the latest Tropical Weather Outlook for more information. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends across parts of Panama and Costa Rica and continues from 10N86W to 09N90W to 09N100W. The ITCZ extends from 09N100W to 07N110W to 10N116W, then resumes at 12N124W to a low pressure near 12N133w to 09N140W. Scattered moderate convection is from 09N to 11N between 102W and 107W, and from 11N to 13N between 130W and 135W. ...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 based on an altimeter pass. Aside from the Gulf of Tehuantepec region, the ridge will remain in place during the next few days with little change in winds and seas. High pressure over the Great Basin region is supporting moderate to fresh northwest winds over the northern and central Gulf of California, with seas nearing 4 to 5 ft. The high pressure will then shift eastward on Tuesday which will help to decrease winds over this 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 the middle of the week, with seas of 6 to 7 ft. Light and variable winds and seas of 4-6 ft in SW swell will prevail N of the monsoon trough, while gentle to moderate SW to W winds and seas of 5-7 ft aslo in SW swell will prevail S of the trough. Little change is expected with these marine conditions through midweek. Swells originating in the Gulf of Tehuantepec (where a gale force gap wind event is expected) will reach the offshore waters of Guatemala and El Salvador building seas to 8 to 10 ft tonight through Wednesday. REMAINDER OF THE AREA... Please see the Special Features section above for more information on low pressure centered near 19N122W. Elsewhere, high pressure located N of Hawaii extends a ridge SE across the N waters to near 25N115W. Cross equatorial southwesterly swell will continue to propagate across the south-central waters, particularly S of 15N between 100W-130W through late today, with seas of 8 to 9 ft. The aerial extent of the 8 ft seas or greater will disminish on Tuesday, and by Tuesday night seas of 5-7 ft will dominate most of the waters W of 110W. Looking ahead...a cold front is forecast by the computer models to reach the far NW corner of the forecast region by Thursday night while weakening. A significant swell event will follow the front, with seas building to 10 to 16 ft over the NW waters by Friday. $$ GR