000 AXPZ20 KNHC 132215 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Tue Dec 13 2016 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 2130 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N77W to 08N79W to low pressure near 10N93.5W to 08N98W. The ITCZ continues from 08N98W to 10N119W to 13N130W...then resumes near 10.5N134W to beyond 09.5N140W. Scattered moderate convection is from 04N to 07N between 77W and 85W. Scattered moderate convection is from 10N to 14N between 92W and 95W. Scattered moderate convection is within 90 NM either side of the axis between 97W and 130W. Scattered strong convection is noted from 07.5N to 10.5N west of 136W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Strong northerly winds across and downstream of the Gulf of Tehuantepec to 14.5N earlier today have diminished to less than 20 kt this afternoon, and are expected to become light and variable this evening. A modest high pressure ridge across the SW Gulf of Mexico will maintain enough pressure gradient to produce fresh to strong N to NE winds returning late tonight through Wed over the Gulf of Tehuantepec. A new cold front will sink across the northern Gulf of Mexico on Wed with reinforcing high pressure to strengthen the drainage winds over the Gulf of Tehuantepec Wed night through the remainder of the work week. Near gale force winds appear to be in the offing for Thursday evening through Friday as a result. A stronger cold front could produce a gale wind event beginning on Monday. Moderate northwest winds over the offshore waters north of 20N will become gentle to moderate through Thursday night with 3-5 ft seas prevailing. A cold front will move into the area from the west, and extend from near San Diego, CA to 26N121.5W by Friday evening. The front will then sweep southeastward across the Baja Peninsula and NW Mexico and pass south of the Baja Peninsula by Saturday evening. Model guidance shows strong southwest to west winds ahead of the front and strong to near- gale force west to northwest winds behind the front over the Gulf of California on Friday night. Fresh to strong NW winds will affect the offshore zones N of 25N on Saturday and Saturday night, with seas building as high as 11 ft near 30N. Gentle to moderate north to northwest winds will prevail south of Mazatlan through Wednesday, becoming light Thursday through Saturday. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... A weak 1011 mb surface low currently centered south of Tehuantepec near 10N93.5W will move westward away from the forecast area through Thursday night, where global models indicate gradual opening up of the low to a trough for the next several days. Latest observations and global model forecasts suggest easterly winds of 20 to 25 kt across the northern semicircle of the low this afternoon and evening before winds begin to slowly diminish to around 20 kt during the next day or so. REMAINDER OF THE AREA... Broad high pressure of 1022 mb near 31.5N122W continues to reside over the northern waters. Gentle to moderate north- northwest winds are expected east of the high through Wednesday. A trough of low pressure is moving westward across west portions of the trade wind belt, located from 10N133.5W to 15N132. The pressure gradient between the high and the north side of the trough is generating NE to E winds of 20 to 25 kt and seas to 8 ft from 14N to 17N between 128W and 132W. The trough is expected to gradually weaken as it translates west and then northwestward during the 24 to 3 hours. Associated winds and seas will subside. The remnants of this trough will gradually lift northwest Thu through Fri, ahead of low pressure and a trailing frontal boundary currently lurking west-northwest of the area. The front will enter the far NW waters on Wed. South to southwest winds of 20 to 25 kt and 8-10 ft seas will precede the boundary. Reinforcing cold air will push the front east- southeastward across the northern waters Thursday and Friday. NW swell generated behind the front will cause seas north of 25N and west of 120W to build to 8-10 feet by Friday. Seas east of 130W will briefly subside to around 8 ft on Saturday before a round of reinforcing N swell arrives on Sunday. $$ Stripling