000 AXPZ20 KNHC 222154 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2154 UTC Thu Sep 22 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 1800 UTC surface analysis and satellite imagery through 0000 UTC. ...SPECIAL FEATURES... Broad and elongated low pressure centered within the monsoon trough approximately 740 nm south of the southern tip of the Baja California peninsula. A recent scatterometer pass indicated the main circulation is centered near 11N115W, with sharp turning along the monsoon trough 12N112W. Fresh southwest winds are evident converging into the monsoon trough from 07N to 10N between 111W and 117W. Concurrent altimeter data indicated seas of 8 to 10 ft along roughly 112W from 04N to 15N. Numerous moderate to isolated strong convection is noted from 07N to 13N between 110W and 125W. A gale warning is in effect beginning late Friday night as the low pressure approaches near 13N114W with 30 to 35 kt winds within 60 nm in the northeast semicircle of the low along with seas of 9 to 13 ft. By early on Saturday, the low is forecast to be near 15N115W with gale winds of 30 to 35 kt within 60 nm of the low and seas building up to 14 ft, or possibly higher. The global models depict the low to track northwestward through Saturday, then curve north to north-northeast on Sunday and Monday. This system has a high chance of becoming a tropical cyclone during the next 48 hours, and through the next 5 days. Please refer to the latest Graphical Tropical Weather Outlook for more information at http://hurricanes.gov. ...TROPICAL WAVES... A tropical wave axis is along 85W north of 06N moving west at 10 to 15 kt. No significant convection is noted currently near the tropical wave, but it will likely enhance overnight showers and thunderstorms off the northern Central American coast. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N86W to 1007 mb low pressure centered near 11N115W to 1011 mb low pressure centered near 13N127W to 11N135w to 1012 mb low pressure centered near 13N140W. Scattered moderate convection is centered within 120 nm north of the monsoon trough axis between 94W and 96W, and within 90 nm north of the axis between 125W and 129W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Scattered showers and thunderstorms persist over the southern Gulf of California this afternoon. This is related to divergentwinds in the high levels of the atmosphere between an upper low over west central Mexico and an upper anticyclone centered near 23N120W. This activity will persist tonight over the waters off Jalisco and Colima states as the upper low shifts west. Winds and seas have diminished this afternoon in the Gulf of Tehuantepec, after an overnight pulse of 15 to 20 kt gap winds with seas approaching 8 ft. No significant gap winds are expected through the Gulf of Tehuantepec through early next week. Elsewhere gentle to moderate winds persist with 4 to 6 ft seas over open waters and 2 to 4 ft seas in the Gulf of California. Seas will build off Baja California Norte this evening as the leading edge of 8 to 10 ft northerly swell pushes into the region. Swell in excess of 8 ft will reach as far south as the northern coast of Baja California Sur by late Friday, before starting to decay from south to north through Saturday. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate to occasionally fresh winds will prevail north of the monsoon trough, while gentle to moderate southwest winds are expected south of the monsoon trough. Seas will remain near 7 ft through Friday as long period southwest swell propagates into the region. Seas will begin to subside on Saturday and lower to between 4 and 6 ft on Monday. REMAINDER OF THE AREA... A 1011 mb low pressure along the monsoon trough near 13N140W will slowly shift west of the area during the next couple of days. Another 1011 mb low pressure area is analyzed along the monsoon trough near 13N127W. Scattered showers and thunderstorms are active with 60 nm in the northwest quadrant of the low pressure, where an earlier scatterometer pass indicated 20 to 25 kt winds. A concurrent altimeter pass indicated seas to 8 ft. Winds and seas associated with this low pressure area will diminish as the low is expected to weaken and dissipate over the next 24 to 36 hours. Meanwhile, a surface ridge extends from a 1029 mb high center well north of the area near 35N136W southeastward toward the southern tip of the Baja California peninsula. The difference in pressure between the ridge and the lower pressure farther south along the monsoon trough is generating moderate trades west of 120W between 15N and 25N. Trades are moderate to fresh west of 120W and north of 25N with seas in the range of around 5 to 7 ft. $$ CHRISTENSEN