000 AXPZ20 KNHC 120900 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0900 UTC Wed Oct 12 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 0600 UTC surface analysis and satellite imagery through 0830 UTC. ...SPECIAL FEATURES... A gale warning remains in effect for the Gulf of Tehuantepec for early this morning. A scatterometer pass from 04 UTC indicated winds to 30 kt, and winds to gale force are possible before dawn given the added component of localized nocturnal drainage flow. The gales are a result of fairly tight pressure gradient between high pressure over east central Mexico and linger lower pressure south of the area in the tropical eastern Pacific. Winds will diminish later this morning as overnight drainage flow effects taper off, but another round of at least near-gale force winds are possible tonight into Thursday morning in the Gulf of Tehuantepec. Strong gap winds will pulse again Thursday night, although not as strong as ongoing currently. The overall pattern will improve as high pressure north of the area weakens, and only 20 kt gap winds are anticipated by Fri night. ...TROPICAL WAVE... A tropical wave is moving off the coast of Nicaragua and northwest Costa Rica into the eastern Pacific, centered near 87W from 08N to 13N, and is enhancing overnight convection off the coast of El Salvador. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N87W TO low pressure near 11N104W to 09N108W to 15N120W to beyond 08N140W. Scattered moderate to isolated strong convection is occurring within 210 nm north of the monsoon trough between 101W and 109W. Scattered moderate convection is noted within 90 nm south of the monsoon trough between 118W and 122W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A ridge extends from 1021 mb high pressure centered west of the area near 31N132W to the southern tip of the Baja California peninsula, supporting moderate northwest to north winds off the Baja coast currently. These winds will increase to 15 to 20 kt by late today as the ridge builds slightly eastward. The high pressure will weak Thursday ahead of a frontal boundary moving into the northeast Pacific, allowing the winds to diminish. 4 to 6 ft seas will persist off Baja into Friday. Looking ahead, long period northwest swell will push into the waters off Baja California Norte by late Friday and Baja California Sur Friday night, with seas building to 9 ft. Winds to 25 kt with seas to 11 ft are possible off the northern portion of Baja California Norte by late Saturday as well as the ridge builds eastward again. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gentle to moderate southwest winds persist south of the monsoon through...including the waters between Ecuador and the Galapagos Islands. Seas are 4 to 6 ft south of the monsoon trough largely associated with long period southwest swell. These marine conditions will change little over the next few days. REMAINDER OF THE AREA... Showers and thunderstorms near a 1008 mb low pressure area centered near 18N124W have almost dissipated over the past several hours as the low pressure moves into cooler waters and encounters stronger wind shear aloft. Chance of any significant development are dropping fast, and the low pressure will likely open into a surface trough later today as it continues to move to the northwest. Fresh to strong winds are still likely within 210 nm to the north of the center at least through today into tonight. Seas of 8 to 10 ft are likely to persist as well, although this is in part due to incipient northwest swell already in the area. A second low pressure area is centered near 11N103W. While moderateto strong convection persists on the northern portion of this low pressure, recent scatterometer passes indicate this may not be a closed circulation at the surface. This low is expected to continue west along the monsoon trough and cross Clipperton Island near 110W later today. Thereafter, the low may weaken somewhat, although a there is a moderate chance of tropical cyclone development through the end of the week as the low pressure continues westward, reaching late 120W Thursday and 125W by Friday. Elsewhere, a relatively weak subtropical ridge to the north is maintaining generally moderate trade wind flow across the region outside of the two low pressure areas mentioned above. Most of the 8 to 9 ft northwest swell covering an area from 12N to 22N between 125W and 130W will subside below 8 ft later today. However a new round of long period northwest swell will move into the region late today and tonight, covering the area northwest of a line from 30N125W to 14N140W, with 8 to 12 ft seas, highest to the northwest. The leading edge of 8 ft swell will reach from the coast of Baja California Norte to 10N140W by late Friday, and cover most of the region north of 08N and west of 110W by late Saturday. $$ CHRISTENSEN