000 AXPZ20 KNHC 150353 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Thu Dec 15 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 0000 UTC surface analysis and satellite imagery through 0230 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec...A Gale Warning is in effect for the Gulf of Tehuantepec beginning Thursday evening. This afternoon and evening, northerly winds in the 20-25 kt range were noted across the Gulf, with seas of 5-7 ft. Winds will further increase to 30 kt tonight, with seas building to 8 ft in and downstream of the Gulf. A cold front moving across the Gulf of Mexico on Thursday will allow northerly winds behind the front to begin to spill through the Isthmus of Tehuantepec and across the Gulf of Tehuantepec. Winds across these Pacific waters are forecast to reach minimal gale force Thursday evening through Friday morning, while seas are forecast to build to 9-11 ft with this gap wind event. A stronger cold front could produce a more significant northerly gale wind event beginning on Monday. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N75W to low pressure near 09N99.5W. The ITCZ extends from 09N100W to 10.5N128W to beyond 10N140W. Widely scattered moderate isolated strong convection noted from 08N to 12N between 94W and 102W. Scattered moderate to strong convection is noted within 120 nm N and 60 nm S of the ITCZ between 116W and 121W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: see Special Features section above for details. Gentle to moderate northerly winds and seas of 4-5 ft continue over the offshore waters W of Baja California this evening, under the influence of a ridge anchored by a 1019 mb high pressure center located near 31N121.5W. The high will weaken over the next couple of days as a cold front moves eastward across the N waters. The front, currently stalled across the far NW portion of the discussion area, is forecast to approach northern Baja California on Friday and move across the area, including the northern part of the Gulf of California, Friday night. Expect increasing winds ahead and behind this front. Model guidance suggests strong southwest to west winds ahead of the front and strong to near-gale force west to northwest winds behind the front over the northern Gulf of California Friday night into Saturday morning. Fresh to strong NW winds will affect the offshore zones N of 25N on Saturday and N of 22N Saturday evening, with seas building as high as 10 ft near 30N behind the front. Outside of the Gulf of Tehuantepec area, mainly light to gentle winds prevail south of Cabo Corrientes, with seas of 3-4 ft. These marine conditions will persist over the next couple of days. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... A 1010 mb low pressure center, currently centered southwest of Tehuantepec near 09N99.5W, will continue to move westward and away from the offshore waters while opening up into a trough by Thursday. Widely scattered moderate to strong convection is noted about the circulation of this low, from 08N to 12N between 94W and 102W. This active weather should continue through the overnight hours. Fresh to strong NE winds and building seas to near 8 ft are expected across the Gulf of Papagayo E of 89W beginning late tonight through early Thursday morning, then persisting through Friday morning. A larger gap wind event appears to be in store for most of zone PMZ113 on Tuesday morning as strong trade wind flow in the SW Caribbean funnels across Central America. REMAINDER OF THE AREA... A cold front has already reached the NW waters and has briefly stalled from 30N136W to 24N140W. Fresh to strong S-SW winds are observed north of 28N east of the front to 131W, where seas are running 7-9 ft. The front will move eastward across the N waters, reaching Baja California Norte by Friday night. Winds are forecast to diminish to 20 kt or less ahead of the front by Thursday night, then will increase again ahead and behind the front Friday night into Saturday morning as a strong high pressure builds across the forecast waters in the wake of the front. N swell generated behind the front will cause seas to build to 8-10 feet across the far NW waters tonight into Thursday. Seas east of 130W will briefly subside to around 8 ft on Saturday before a round of reinforcing N swell arrives on Sunday. High pressure building N of the area will cause a large area of fresh to strong trades to develop N of the ITCZ from 07N to 25N W of 125W by Tuesday morning. Seas in this area will be build to the 8 to 11 foot range. As previously mentioned, a 1019 mb high pressure is centered near 31N121.5W and extends a ridge across the NE waters. The pressure gradient between the ridge and a surface low near 21.5N132.5W is producing an area of fresh to strong E to S winds within 150 nm across the eastern semicircle of the low. The low will shift north northeastward over the next 24 hours, ahead of the approaching cold front across the NW waters, and weaken to an open trough, gradually merging with the southerly winds occurring east of the front. Expect increasing trade winds and building seas across the west- central waters during the upcoming weekend as strong high pressure builds N of area. $$ Stripling