000 AXPZ20 KNHC 302121 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sat Sep 30 2017 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 2100 UTC. ..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends across Central America near 12N87W to a 1010 MB low pres near 12N110W to 1010 MB low pres near 11N131W to beyond 10N140W. Scattered moderate convection is from 05N to 10N between 81W and 92W. Scattered moderate isolated strong convection is from 07N to 09N between 92W and 95W, and from 09.5N to 11N between 101W and 104W. Similar convection is from 10N to 12N between 130W and 132W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Fresh to locally strong gap winds will develop over the Gulf of Tehuantepec during the overnight and early morning hours beginning tonight, and will continue through Tuesday as a ridge persists across the western Gulf of Mexico and the eastern slopes of the Sierra Madre Mountains. Seas will build to 6-7 ft through early Monday morning, and to 7-8 ft by early Tuesday morning. Marine guidance suggests increasing winds and building seas across the Tehuantepec area as an area of low pressure develops a few hundred miles south of the southern coast of Mexico or Guatemala, near the Gulf of Tehuantepec, by the middle of next week. Environmental conditions are expected to be conducive for gradual development of this system while it moves slowly west- northwestward or northwestward. Elsewhere, a ridge dominates the waters west of the Baja California Peninsula producing gentle to moderate northerly winds and seas of 4-5 ft. Northerly swell will propagate into the waters west of Baja California Norte starting Sunday morning, building seas to 6-8 ft Monday through Tuesday. Fresh to locally strong S-SW winds are expected over the northern Gulf of California Sunday night through Tuesday as low pressure develops over the area. Seas are forecast to build to 5-6 ft over the northern Gulf with these winds. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... An active monsoon trough is currently across Central America and adjacent waters. The trough will remain close enough to the coast, either inland or just offshore, to produce active convection, primarily during the late afternoon and evening hours, over portions of Central America as well as the adjacent coastal waters during the next few days. Winds are on the increase south of the monsoon trough with seas building seas to 8 ft. Winds and seas are forecast to further increase south of the monsoon trough through at least the middle of next week. As a result, fresh to strong SW to W winds and seas of 10-11 ft will affect the waters beyond 200 nm off the coast from Nicaragua to Guatemala beginning Monday morning. A fresh SW swell train, with a leading edge period of 20 to 22 seconds is forecast to reach the waters between Ecuador and the Galapagos Islands Tuesday night, building seas to 7-8 ft by Wednesday night, and to 8-10 ft by Thursday. REMAINDER OF THE AREA... A 1027 mb high pressure located N of area near 38N131W extends a ridge across the waters N of 20N. The pressure gradient between the ridge and the monsoon trough is supporting moderate to locally fresh NE winds from 18N to 26N W of 130W based on scattermeter data and a few ship observations. The high pressure center is forecast to move SW over the next 24 hours, reaching a position near 36N134W. The pressure gradient between the high and lower pressure inland over the SW of U.S., and NW Mexico will produce N winds of 20-25 kt across the waters N of 28N between 122W and 128W by Sunday night, and N of 27N between 122W and 130W on Monday. These winds combined with northerly swell propagating into the waters north of 25N between 120W and 130W Sun through Mon night, will build seas to near 12 ft along 30N by Monday. Farther south, cross equatorial southerly swell will propagate across the waters south of 02N between 105W and 135W by Tuesday, with seas building to 8-10 ft. $$ GR