000 AXPZ20 KNHC 181002 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Wed Jan 18 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 0600 UTC surface analysis and satellite imagery through 0930 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A meandering trough extends from 05N77W TO 02N79W to 03N90W. The ITCZ axis extends from low pressure near 05N93W 1012 mb to 03N103W to 03N110W to 08N118W where it briefly ends. It resumes at 08N122W to 06N130W to 05N140W. Scattered moderate isolated strong convection is seen within 180 to 240 nm north of the axis between 112W and 118W, and also within 60 nm north of the axis between 122W and 127W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Satellite water vapor imagery shows an upper level trough extending from a deep layered cut-off low pressure system across the central portion of SW New Mexico southwestward to far NW Mexico, and continuing to across Baja California Norte and to beyond 19N120W. An upper level jetstream branch is moving through the base of this trough from 18N120W northeast to 24N110W and to over west-central Mexico at 25.5N108W. It continues well inland to over much of northern Mexico and into SE Texas. The imagery depicts a 450 nm wide moisture plume consisting of mid and upper level clouds located to the southeast of the jet stream branch. The strong southwest jet stream winds are advecting these clouds northeastward towards much of central Mexico. Jetstream energy is sufficiently available, and will combine with the deep moisture to produce scattered showers and isolated thunderstorms offshore the Mexican coast from near Manzanillo north to just south of Baja California Sur and the coast of Mexico near Los Mochis. Similar activity is very possible inland the Mexican coast between these two locations to well inland across the Sierra Madre Occidental mountains. Gentle to moderate northwest to north winds prevail off the coast of Baja California and in the Gulf of California per the Ascat pass from 0514Z, and from a couple of ship observations noted along the ocean side of the Baja California coast. Light to gentle northerly winds prevail south and east of Acapulco. Seas across the area are running 5-6 ft west of Baja California, 1-3 ft in the Gulf of California, and 3-5 ft elsewhere. Global models indicate a cold front will move into the waters off Baja California Norte Thursday, then become diffuse ahead of a much stronger cold front that will quickly move in across Baja California and the Gulf of California Friday and Saturday. The second cold front will be accompanied by fresh to strong winds and large northwest swell. This swell event is expected to build seas to the range of 12-19 ft in the waters off Baja California Norte Saturday, and 8-13 ft seas off Baja California Sur. Wave model guidance actually indicates that seas may max out higher to around 21 ft in the waters north of 29.5N on Saturday. These marine conditions are likely to bring hazardous marine conditions to mariners navigating the nearshore and coastal waters, and very dangerous surf conditions along the coasts and beaches. Southwest winds ahead of the second cold front are expected to increase to near gale force over much of the northern portion of the Gulf of California Friday night into Saturday, with seas possibly building to 8-9 ft, quite impressive for those waters. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate northwest winds this afternoon will pulse to 25 kt late tonight through Wednesday morning, and then again briefly late Wednesday night across the Gulf of Papagayo and downwind to about 89W. Winds area then expected to diminish by Thursday night. Light to gentle variable winds are expected there Friday. Light to gentle easterly winds will prevail elsewhere through Saturday. Seas will be generally 3-5 ft in the forecast waters. REMAINDER OF THE AREA... A 1024 mb high pressure centered at 26.5N135W extends a ridge southeast to the vicinity of Cabo Corrientes. The gradient between this high and lower pressure associated with the ITCZ is supporting an area of fresh to strong northeast trade winds from 10N TO 16N west of 130W and from 12N to 14N between 122W and 133W, with seas in the range of 9-11 ft. Fresh trades are found elsewhere roughly from 07N to 19N west of 133W, and from 10N to 15N between 116W and 133W per the 0510Z Ascat pass. Seas with these trades are in the 8-10 ft range due to mixed northwest swell with northeast windwaves. Fresh trades will remain from 07N to 20N west of 122W, with 8-10 ft seas in mixed NE and NW swell. The 1024 mb high will be nudged to the southwest over the next few days in response to the aforementioned cold fronts forecast to pass across the waters north of 25N. This will allow for the zone of the strong trades to decrease in coverage and shift westward through Friday. As mentioned above, a very active jet stream branch is rounding the base of the deep layered trough across northwest Mexico. The upper trough will continue to slide eastward through Friday while shearing out, however a stronger trough will quickly sweep southeastward, and merge into the first trough on Thursday. High pressure will build eastward behind the previously mentioned cold fronts, with associated moisture and weather shifting eastward with it. Looking ahead, northwest swell with seas to 8-16 ft associated with a cold front moving eastward across the waters north of 25N through Thursday will be followed by a second front expected to sweep southeastward across the northern waters Thursday night and Friday. Wave model guidance shows large northwest swell will propagate southeastward into the waters north of 20N behind the second front, with seas building quite large to 15-21 ft in the far northern waters east of 130W late Friday into Saturday. $$ AGUIRRE