000 AXPZ20 KNHC 132209 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Thu Dec 13 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 1800 UTC surface analysis and satellite imagery through 2030 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A cold front forecast to enter the NW Gulf of Mexico this evening will initiate gale to strong gale force winds across the Gulf of Tehuantepec by Fri evening and is then expected to persist through the upcoming weekend and beyond. Computer model guidance suggests that this long lived gale event will last until Mon afternoon. Peak winds are forecast to be 40 kt on Sat as corresponding seas quickly building to near 18 ft. The first blast of strong northerly winds associated with this event is expected to start during Fri afternoon. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N75W TO 03.5N78.5W TO 08.5N85W TO 05N102W. The ITCZ continues from 05N102W TO 08.5N118W TO 10N134W to beyond 07N140W. Scattered moderate to strong convection is observed from 01.5N to 05.5N to the east of 85W, while scattered moderate convection is observed from 04.5N to 07N between 92W and 102W. An upper level trough across far NW portions of the area is creating a large area of overcast middle and high level clouds, and scattered light to moderate elevated convection from 15N to 22N between 120W and 136W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Over the open waters off Baja California, another pulse of NW swell is expected to reach Baja California Norte and Guadalupe Island tonight. This latest round of swell will propagate SE and cause seas to build to between 7 and 11 ft for the offshore waters along the length of the Baja Peninsula by Fri afternoon. A cold front approaching 30N140W late tonight will introduce more long period NW swell to Baja Waters by Sun morning and maintain sea heights at 7-9 ft through Mon morning. Looking ahead, a much stronger cold front will reach Baja California Norte by Mon night. Strong winds associated with this front could brush 30N as the front crosses 30N140W. Long period NW swell of 10-18 ft will enter the waters adjacent to Baja California Norte during this time frame. Swell of this size and period will present hazard seas for mariners as well as cause very powerful and dangerous surf along the Pacific Beaches. Strong high pressure building over the Great Basin will support the development of fresh to strong winds over the Gulf of California between 25N and 29N this afternoon through Fri morning. seas could approach 8 ft over the southern Gulf tonight. Winds and seas will subside through Sat as the high pressure shifts eastward. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo...Strong gap winds have tapered off today but will return during the overnight and early morning hours Sat night, then persist through Mon night as high pressure builds north of the region. Seas are expected to max out around 10 ft on Sun. Gulf of Panama...Fresh northerly winds across and downstream of the Gulf have begun to back to the NW this afternoon and will slowly diminish through Sat. Elsewhere, gentle to moderate winds will persist on either side of the monsoon trough through the remainder of the week, with seas remaining in the 4-6 ft range. REMAINDER OF THE AREA... A large area of mixed seas persists over much of the north Pacific between 95W and 120W. This area consists of NE and E swell generated by recent Central American gap wind events, merging with longer period NW swell. Maximum combined sea heights in this area are 10 ft. This area of 8 ft seas will vanish by late tonight as these swell decay. Farther west, a persistent surface trough extends from 08N139W TO 16N134W. The gradient between this trough and high pressure north of the region is supporting strong trade winds from 15N to 20N between 125W and 140W. Recent satellite-derived wave height data indicate seas as high as 13 ft. The high will weaken today ahead of an approaching cold front, allowing the trade winds to diminish by Fri morning. A cold front will reach from 30N135W to 28N140W by early Fri, and be accompanied by a new round of NW swell of 12 to 15 ft. The front will dissipate later on Fri, with the swell subsiding as well. Elsewhere NW swell in excess of 8 ft will more or less dominate the waters west of 110W through Sun. Very large NW swell, in excess of 20 ft, will enter NW portions of the forecast area early Sun in conjunction with the arrival of a strong cold front. Seas of 12 ft or above could encompass almost all of the forecast waters N of 07N and W of 115W by Tue morning. $$ Stripling