000 AXPZ20 KNHC 030817 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Tue Nov 3 2020 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 0800 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Recent scatterometer passes indicate gap winds over the Gulf of Tehuantepec are at gale force, down from earlier storm force winds. Wave heights in the middle of this plume remain near 25 ft. The gales are due to a tight pressure gradient created by high pressure building north of the area over the Gulf of Mexico and across the eastern slopes of the Sierra Madre Oriental mountains. Swell generated from this event will produce a large plume of 12 ft or greater seas that will extend about 500 nm southwest of the Gulf of Tehuantepec. Winds will gradually taper off to below gale force by early Fri, as the high pressure north of the area weakens and shifts east. Marine interests transiting across or in the vicinity the Gulf of Tehuantepec should be aware of this gap wind event, and take necessary action to avoid hazardous marine conditions over the affected waters. Please refer to the latest High Seas Forecast issued by the National Hurricane Center at: https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml for further details. Potential Heavy Rainfall event: Hurricane Eta over the western Caribbean along with a surge of moist southwesterly flow across the tropical eastern Pacific will support heavy to torrential rainfall across portions of Central America through mid week. Eta is likely to cause life- threatening flash flooding and river flooding across portions of Central America, along with landslides in areas of higher terrain. Eta is expected to produce rainfall accumulations of 15 to 30 inches (375 to 750 mm) across central and northern Nicaragua into Honduras, with isolated amounts of 35 inches (890 mm). Refer to statements provided by your national meteorological service for more details. 1008 mb low pressure continues to develop where a tropical wave along 115W intersects the monsoon trough near 12N115W. Scattered moderate to isolated strong convection and thunderstorms are from 10N to 16N between 111W and 118W. Recent scatterometer satellite data indicates the low is still fairly elongated from east to west along the monsoon trough, but also that nearby winds are in excess of 25 kt. A concurrent altimeter satellite pass indicates seas of at least 8 to 10 ft. Environmental conditions remain favorable for further development, and a tropical depression is likely to form during the next two days as the system moves west- northwestward or northwestward, well offshore of the coast of Mexico. There is a high chance the low will develop into a tropical depression over the next 48 hours. ...TROPICAL WAVES... See special features section above for information on a tropical wave with potential to develop into a tropical cyclone within the next two days. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 11N85W to 07N98W to 12N108W to 1008 mb low pressure near 12N115W to 09N140W. Scattered moderate isolated strong convection is observed from 08N to 11N, between 103W and 106W. Scattered moderate convection from 08N to 10N between 123W and 125W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please refer to the Special Features section above for details on the Gulf of Tehuantepec Storm Warning. Of note, the 20-year climatology of the Tehuantepec gap wind events indicates that most gale-force events occurred during November and December while most storm-force winds occurred in January. Based on records, the first storm-force winds event usually occurs toward mid-November each cold season. A ridge northwest of Baja California is supporting gentle to moderate northerly winds with seas 3 to 5 ft. Seas will build to 8 ft near the Revillagigedo Islands on Wed as a low pressure with potential to become a tropical cyclone moves to its closes point of approach to the islands and it moves west-northwestward. Seas will build to 4 to 6 ft elsewhere off Baja California after mid week in a mix of NW swell and shorter period southerly swell emerging from the developing low pressure. A cold front may bring strong NW winds to the waters off Baja California Norte and the Gulf of California Fri night. Gentle winds will persist south of Cabo Corrientes outside of the Gulf of Tehuantepec plume, with seas of 4 to 6 ft in mostly southerly swell. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... Moderate to locally fresh south to southwest winds are south of the monsoon trough. Large seas generated by the storm gap wind event in the Tehuantepec region are propagating across the offshore waters of Guatemala and El Salvador, mixing with SW swell. Farther south, a combination of fresh SW winds and building SW swell support seas to 8 ft off western Panama and near the Azuero peninsula. As Hurricane Eta approaches the Caribbean coast of Nicaragua tonight, expect increasing SW flow across the offshore forecast waters of Costa Rica and Panama, including the Gulf of Panama. REMAINDER OF THE AREA... High pressure dominates north of 20N, anchored by 1022 mb high pressure centered near 27N133W. A stationary front is dissipating near 30N140W. This pattern is supporting gentle to moderate NE winds over most area north of the monsoon trough, with isolated areas of fresh trades closer to the monsoon trough. Seas are 4 to 6 ft except for near the low pressure mentioned in the Special Features section, and in an area of building seas between 15N to 20N west of 135W related to a large area of fresh trade winds farther west. Seas are also reaching 8 to 9 ft due to NW swell near the dissipating front at 30N140W. Farther east, seas are 8 to 12 ft over tropical waters east of 110W due to NE swell emerging out of Tehuantepec and longer period SW swell moving into the region. The current trends will persist through mid week. By late in the week, the low pressure area will likely be weakening over cooler waters west-northwest of the Revillagigedo Islands. Lingering swell from the low will mix with a new batch of NW swell expected to invade the waters north of 20N. Seas may reach as high as 14 ft in this NW swell north of 20N and east of 125W, following a strong front expected to move into the area. Meanwhile east of 120W, gale to storm force wind event in Tehuantepec will finally be tapering off by Fri, with related seas subsiding accordingly. SW swell will persist however. $$ Christensen