000 AXPZ20 KNHC 151517 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1510 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 1200 UTC surface analysis and satellite imagery through 1400 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 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. This gap wind event is expected to continue through at least midweek. Seas will reach 13 to 15 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 15N117.5W. 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 13N to 20N between 115W and 120W. 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 re-analyzed near 89W N of 05N, moving westward at around 10 kt. Scattered moderate convection is from 07N to 13N between 90W and 93W. This convection is also occurring in part due to the nearby monsoon trough. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N78W to 07N101W, then transitions to an ITCZ axis and continues to 13N114W. The monsoon trough then resumes southwest of the special features low near 13N119W and continues to a 1007 mb low pres near 10N131W to 09N140W. Aside from convection associated with the tropical wave. Scattered moderate and isolated strong convection are from 08N to 12N between 95W and 102W, from 07N to 11N between 118W and 122W, and within 90 nm of either side of the monsoon trough axis W of 128W. ...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 4 to 6 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 fresh to locally strong northwest to north 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 Wednesday. 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 special features section above for more information on low pressure centered near 15N117.5W. Elsewhere, high pressure of 1034 mb centered NW of the area near 38N151W has an axis that extends southeast to near 25N118W. 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 W of a line from 28N140W to 18N110W to 08N110W to the Equator near 103W. 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 monsoon trough. 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 trough 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 8 to 16 ft by Friday over those waters. $$ Latto