000 AXPZ20 KNHC 152128 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2127 UTC Sun Oct 15 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 1800 UTC surface analysis and satellite imagery through 2115 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Northerly winds of 20 to 30 kt over the Gulf of Tehuantepec will increase to minimal gale force by early Monday morning as a high pressure builds over the eastern slopes of the Sierra Madre in Mexico and the western Gulf of Mexico in the wake of a cold front. This event is expected to continue through at least midweek. Seas will reach 12 to 14 ft during the overnight and early morning hours when winds peak near 40 kt Monday night. A low pressure of 1006 mb is centered near 16N119W. Winds of 20 to 25 kt are occurring along the eastern side of a trough axis extending north and south of the low. Numerous moderate to strong convection are from 14N to 21N between 116W and 121W. This system is gradually becoming better defined, and environmental conditions appear conducive for a tropical depression to form during the next day or so while the system moves west- northwestward to northwestward at around 10 kt. There is currently a high 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. ...TROPICAL WAVES... The axis of a subtle tropical wave has been analyzed along 93W and N of 05N, moving westward at around 10 kt. Scattered moderate convection is from 08N to 13N between 92W and 100W. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N86W to 09N96W, then transitions to an ITCZ and continues to 08N115W. The ITCZ then resumes southwest of the Special Features' low near 11N123W and continues to a 1008 mb low pres near 11N132W to 09N140W. Aside from convection associated with the tropical wave, scattered moderate convection is from 06N to 13N and west of 129W. ...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 3 to 5 ft. 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 building over the Great Basin region is supporting moderate to fresh northwest winds over the northern Gulf of California today, with seas nearing 4 to 5 ft. These winds and seas will continue through early Monday, spreading as far south as 26N tonight. The area of high pressure will then shift eastward which will help to decrease winds over this area for the middle of the week. 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 will prevail N of the monsoon trough, while gentle to moderate SW to W winds 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 9 to 10 ft Monday night and Tuesday. REMAINDER OF THE AREA... Please see the Special Features section above for more information on low pressure centered near 16N119W. Elsewhere, high pressure of 1033 mb centered NW of the area near 37N152W extends its axis southeast to near 27N116W. Winds range from moderate over the northern waters, to fresh just north of the monsoon trough. Northerly swell continues to propagate across these waters, mixing with southerly swell over the southern waters, with seas of 8 to 10 ft SW of a line from 24N140W TO 07N111W TO 05N99W TO 00N95W. The swell will continue to subside across the waters N of 20N W of 120W through this evening, becoming confined to the Special Features' low and another low west of 130W along the ITCZ. Cross equatorial southwesterly swell will continue to propagate across the south-central waters, supporting seas greater than 8 ft S of 15N between 100W and 130W through Tuesday. By Thursday night, forecast models are indicating a cold front will begin to cross the NW waters and will bring with it a significant NW swell event, with seas building to 10 to 16 ft by Friday over this area. $$ ERA