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Eastern North Pacific Tropical Weather Discussion
000 AXPZ20 KNHC 170944 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 944 UTC Thu Jan 17 2019 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 0900 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A trough extends from 05N77W to 04N80W. The intertropical convergence zone continues from 04N80W to 03N100W to 1011 mb low pressure near 07N110W to beyond 07N140W. Scattered moderate thunderstorms is noted within 90 nm in the east quadrant of the low pressure. Elsewhere scattered moderate thunderstorms are observed from 11N to 13N between 110W and 115W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Strong to near-gale force winds are pulsing through the Gulf of Tehuantepec, supporting 8 to 10 ft seas. These pulses will continue into Fri then diminish as the gradient weakens across the region. Fairly tranquil conditions will persist across the Gulf of Tehuantepec and downstream late Fri through late Sat. The pattern will change abruptly Sat night, as a the leading edge of a very strong cold front moves through southern Mexico, across the isthmus of Tehuantepec and into the adjacent waters of the Gulf of Tehuantepec. As high pressure builds behind the front over east central Mexico, and the bulk of the cold air reaches the southern Gulf of Mexico, the initial gale force winds will intensify to a strong gale into Sun morning, possibly reaching minimal storm force. Seas will build accordingly, reaching as high as 24 ft by midday Sun. Meanwhile, a large plume of 25 to 35 kt and seas in excess of 12 ft will push as far as 420 nm to the south-southwest downstream of the Gulf of Tehuantepec. Strong gales will likely persist thereafter into Mon. Marine interests transiting through the Gulf of Tehuantepec Sun into early next week should be aware of this upcoming gap wind event, and take necessary action to avoid hazardous marine conditions over the affected waters. Elsewhere over Mexican offshore waters outside of Tehuantepec...1023 mb high pressure west of Baja California near 28N119W continues to maintain light to gentle breezes across the region north of 25N and gentle to moderate breezes elsewhere. NW swell of 8 to 9 ft persist over open waters beyond 120 nm north of Cabo Corrientes. A weak cold front will move into into northern Baja California Norte this evening. While the front will dissipate as it moves across Baja California and the Gulf of California through Fri, it will be accompanied by a new round long-period NW swell of 12 to 16 ft across the waters off Baja California. High pressure building behind the front will allow fresh to strong NW winds north of Cabo San Lucas late Fri into Sat. Over the Gulf of California, strong high pressure building over the Great Basin north of the area will support fresh to strong NW winds extending the length of the Gulf from Fri night through Sat. The strength, fetch and duration of the winds will be enough to support wave heights to 8 ft in the southern Gulf of California by Sat night. Winds and seas will diminish by Sun as the high pressure weakens and shifts east. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Strong high pressure north of the area will keep gap wind areas active through Fri and Sat. Fresh to strong gap winds persist as far as 300 nm to the W-SW of the Gulf of Papagayo through the next several days. Winds will occasionally pulse to near-gale force during overnight and early morning hours. Seas will build to 8 to 10 ft. Similarly fresh to strong northerly gap winds will impact mainly the western Gulf of Panama extending into the waters south of the Azuero peninsula. These gap winds will diminish Sat and Sat night as the high pressure north of the region supporting them shifts eastward ahead of a strong cold front. New high pressure will build in the wake of the front, supporting another round of even stronger gap winds through the Gulfs of Papagayo and Panama. Winds to gale force are possible through the Gulf of Papagayo Mon night. REMAINDER OF THE AREA... 1009 mb low pressure is centered along the ITCZ near 07N111W moving west at 10 to 15 kt. Observations from a nearby TOGA-TAO buoy along with data from an earlier scatterometer pass showed fresh to strong winds within 90 nm in the northern semicircle of the low pressure. An altimeter satellite pass from 05 UTC confirmed seas as high as 13 ft in the area of strong winds north of the low pressure. Scattered thunderstorms are active within 90 nm to the east of the low pressure. This is an indication the low pressure is experiencing strong westerly shear as it moves west of the upper trough axis that had been sustaining it over the past couple of days. The low will weaken through today, and open into a trough tonight as it reaches 115W. The trough will weaken further as it continues westward along the ITCZ over the next several days. Farther northwest, a weak cold front reaching from 30N130W to 28N140W will weaken through today as it continues to move eastward across the waters north of 28N. The main impact will be a new round of long-period heavy NW swell. An altimeter satellite pass from 0230 UTC showed seas of 15 to 23 ft behind the front entering the northwest portion of the discussion area near 30N140W. While the NW swell will subside somewhat through today as it moves into the region, swell in excess of 12 ft will reinforce existing NW swell of 8 to 10 ft farther south over waters west of 120W through Fri. An area of mixed swell will emerge roughly south of 15N between 95W and 100W, due to the reinforced NW swell, a component of SW swell, and shorter period NE and E swell originating out of the gap areas to the east. A ridge will build by Sat across the waters north of 25N in the wake of the front. This will support a broad area of fresh trade winds farther south into the tropics, with fresh to strong winds developing ahead of the surface trough moving along the ITCZ. The ridge will weaken into Sun, allowing winds and seas to diminish somewhat across the tropics. Seas of 8 to 9 ft will persist however Sun into next week south of 20N west of 135W in a mix of NW swell and remaining windwaves from local trade winds. $$ Christensen