000 AXPZ20 KNHC 180935 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Thu Jan 18 2018 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 0845 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Strong high pressure continues to build southward across eastern Mexico and the western Gulf of Mexico behind yet another cold front, and is supporting a tight pressure gradient across southern Mexico. Gale force winds of 40 to 45 kt prevail across and downwind of Tehuantepec and are expected to continue through the early morning hours of Thu. Winds are then expected to gradually diminish below gale force by Friday afternoon. The resultant plume of northerly swell will continue to propagate well southward of the Gulf of Tehuantepec waters, mixing with long period NW swell to produce seas in excess of 8 ft to near 650 nm due S of Tehuantepec and over 800 nm SW of the there through this morning. Maximum seas tonight will remain around 20 ft near the strongest winds, and gradually subside by the end of the week as the winds diminish. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough axis extends from 07N77W TO 09N86W TO 04N98W. Overnight scatterometer winds suggest a transition to ITCZ from 04N98W continuing on to 06.5N109W to beyond 07N140W. Scattered moderate isolated strong convection is occurring from 04N to 10N between 77W and 86W. Scattered moderate isolated strong convection is within 60 nm of the axis between 90W and 107W. Scattered to locally numerous moderate to strong convection is occurring within 90 nm S and 150 nm N of ITCZ between 108W and 121W, and from 06N to 14N between 121W and 136W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the special features section for information about the ongoing gale warning in the offshore waters of the Gulf of Tehuantepec. In the Gulf of California, light to moderate NW flow is expected across across the entire gulf waters through Friday afternoon. Winds will become southerly Friday evening ahead of an approaching cold front, increasing to fresh to strong in the northern gulf Friday night, then shifting to NW to N behind the front. The front will gradually become ill defined as it moves southward through the gulf during the day Saturday with mainly moderate to fresh northerly flow in its wake for the end of the weekend. The ill defined remnants of the front are expected to push S to the entrance of the gulf by Sun afternoon, when the pressure gradient will begin to tight across the area leading to fresh to strong winds developing across the full length of the gulf Sun evening and night. Elsewhere across the offshore waters of Mexico, large NW swell continues to propagate SE across the waters, with seas of 8-11 ft prevailing, except 5-8 ft between 98W and 105W. This large swell continues to generate high and powerful surf along the coasts and outer reefs of the Baja California peninsula and mainland Mexico, which will continue through Thu, with coastal flooding possible. Another pulse of NW swell will reach the offshore waters off Baja California Norte Thursday night. Seas will peak near 13-15 ft by Friday, while seas of 12 ft or greater will spread across the offshore waters off the entire length of the Baja Peninsula through the upcoming weekend. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Fresh NE gap winds prevailing across the regional waters between Papagayo and Tehuantepec will pulse to strong each night and early morning across the Gulf of Papagayo and other typical gap wind areas through Saturday morning, diminishing thereafter. Elsewhere, mainly light to gentle offshore winds will prevail N of 09N, with light to gentle southerly flow S of 09N. NW swell originating from the gale wind event in the Gulf of Tehuantepec along with longer period NW swell will arrive across the area waters Thursday and Friday, building seas offshore to 5-7 ft. REMAINDER OF THE AREA... Large, long period NW swell continues to propagate SE across the forecast waters, with seas of 8 to 12 ft across the waters W of 100W. A weakening cold front has moved into the far NW portion of the area from 30N136W TO 28N140W, and will continue SE through early Thursday, and be reinforced by building high pressure Thursday evening. Winds NW of the reinforced front will increase to fresh to strong Thursday evening, and shift E and SE with the front as it moves through Baja California Fri and Sat. Strong high pressure behind the front will induce fresh to strong trades gradually spreading across the waters N of 10N W of 110W during the upcoming weekend as the front dissipates across the N central waters. $$ Stripling