000 AXPZ20 KNHC 200347 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 139 UTC Fri Apr 20 2018 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 0000 UTC surface analysis and satellite imagery through 0430 UTC. ...SPECIAL FEATURES... A cold front entering the Gulf of Mexico will usher in high pressure over the northern Gulf of Mexico tonight and Fri. This will tighten the pressure gradient across the Isthmus of Tehuantepec and funnel very strong winds over the Gulf of Tehuantepec. N winds will peak at 40 kt tonight and Fri morning and produce 10 to 14 ft wind-driven seas as far downstream as 11N197W. Winds will diminish and seas will subside below 8 ft by Sat afternoon. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough extends from 08N82W to 06N90W to 06N95W. The ITCZ continues from 06N95W to 07N100W to 07N121W to 06N131W to beyond 06N140W. A large area of active convection is associated with the ITCZ. Scattered moderate and isolated strong convection is present from 06N to 12N between 111W and 126W. Isolated moderate and strong convection is found within 90 nm either side of the trough and ITCZ axis between 92W and 110W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Fresh to strong NW winds and seas of 5 to 7 ft are evident in the offshore waters. A weakening cold front crosses the far northern Baja California and swings out over the Pacific from 30N115.5W to 27N125W to 29N135W. The front will continue weakening as it moves SSE tonight and dissipate Fri. Fresh to strong NW winds can be expected over the waters W of Baja California tonight and Fri as a tight pressure gradient consolidates between a ridge building in behind the front over the northern waters and lower pressure over the SW United States and NW Mexico. NW swell following the front will cause seas to build along the length of the peninsula through Fri night. Winds and seas W of the peninsula will diminish Sat through Mon as the high to the N weakens in response to low pres and an attendant cold front approaching from the NW. Moderate NW winds over the Gulf of California will strengthen on Fri and become fresh over the northern and central Gulf. Winds will subside over the Gulf Sat and Sun as the high weakens slightly and the area of low pressure moves east. See the special features section for details concerning the gale force winds expected for the Gulf of Tehuantepec tonight and Fri morning. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Pulsing fresh to strong nocturnal NE to E winds are expected across and downstream of the Gulf of Papagayo through at least Tue night with seas peaking each night between 8 and 9 ft. Gulf of Panama: Fresh northerly winds and seas of 5 to 7 ft are evident across the Gulf of Panama this evening. Winds will become moderate Fri through Sun, with seas generally running between 4 and 6 ft. Elsewhere, mainly light to gentle winds are expected through Tue as a weak surface trough meanders west of Panama and Colombia. Cross-equatorial swell will mix with residual swell from Papagayo through Fri, and increase seas to 5-7 ft S of 10N. Seas will subside to 3-5 ft by Sun as long period SW swell from the Southern Hemisphere decay. REMAINDER OF THE AREA... High pressure measuring 1030 mb is centered north of the forecast area near 36N134W. The high ridges SE across the northern forecast waters to near the Revillagigedo Islands. The ridge is weakening somewhat this afternoon as a dissipating cold front enters the NE waters. The high will become reinforced by stronger high pressure building in behind the dissipating cold front Fri and Sat. Cross equatorial SW swell moving into the southern forecast waters will affect the waters S of 10N between 95W and 120W tonight. Seas will subside to 8 ft or less across most of this area by midday Fri. Another round of SW swell could cause waters near the equator to build to 8 ft or above by early next week. A surface trough will develop along the ITCZ between 125W and 130W Fri. The pressure gradient between the trough and high pressure to the north will support fresh to strong NE trades N of the ITCZ generally between 10N and 15N W of 125W through Saturday. The combination of these winds, NW swell and SW swell will support combined seas of 8 to 12 ft over these waters into Saturday, expanding N to 30N by Sunday as NW swell propagates into the northern waters. The swell will begin to decay below 8 ft Sunday night before becoming reinforced by another set of NW swell by Monday night. $$ CAM