000 AXPZ20 KNHC 152157 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sun Apr 15 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 1800 UTC surface analysis and satellite imagery through 2115 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Strong high pressure shifted southward along the Sierra Madre Oriental and across the western Gulf of Mexico, behind a strong late season cold front, and has initiated an increasing plume of gale force winds across the Gulf of Tehuantepec. Satellite imagery shows a broad arch cloud shifting southward across the Pacific coastal waters extending to about 300 nm S and SW of Salina Cruz, and indicating the leading edge of strong northerly winds and cooler, drier air. Northerly winds are estimated at 30-40 kt across the Tehuantepec region this afternoon, and will increase to 35-45 kt by this evening. These winds are forecast to persist tonight into Mon morning, then gradually diminish, becoming minimal gale force Tue morning and to only 25 kt by noon time Tue. Seas downwind of the gulf are expected to build as high as 18 to 20 ft tonight into Mon. In addition, an extensive swath of large N to NE swell generated by these northerly winds will propagate well to the SW of the Tehuantepec area, covering roughly the waters from 08N to 14N between 93W and 105W by early Mon morning. Climatologically speaking, the final winter season gale force wind event typically occurs across the Gulf of Tehunatepec in late March or early April. Please refer to the East Pacific High Seas Forecast under AWIPS/WMO headers HSFEP2/FZPN03 KNHC for more details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough extends from 09N73W TO 08.5N85W TO 08.5N96W. The ITCZ stretches from 08.5N96W TO 07N118W TO 08.5N135W TO beyond 08N140W. Scattered moderate to strong convection is noted FROM 04.5N TO 13N BETWEEN 85W AND 111W. Similar convection is noted within 150 nm N and 90 nm S of the ITCZ between 112W and 137W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Moderate to fresh NW to N winds and large NW swell prevail west of Baja California Norte. Seas in the 8-10 ft range continue this afternoon and are forecast to subside to 7-9 ft late this afternoon. The new cold front will sweep across Baja California Norte Monday night and act to freshen wind across the north half of the peninsula through Tue, but otherwise, little change in these marine conditions are expected during the forecast period. Gulf of California: NWly winds continue to gradually diminish this afternoon through the entire length of the Gulf of California, with seas 4-6 ft across the southern waters. Winds will shift S to SW tonight, then, become fresh to strong across the northern Gulf of California Mon through Tue as a low pressure moves across the area. Gulf of Tehuantepec: A strong late season Gulf of Tehuantepec gap wind event induced by a strong cold front moving across the Gulf of Mexico starting early this morning. Please, see Special Features section above for details. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Fresh gap winds are expected across and downstream of the Gulf of Papagayo area tonight, and will increase to strong during the night time hours of Mon through Thu. Gulf of Panama: Moderate to fresh northerly winds are expected across the Gulf of Panama Mon night, and again Wed night. Elsewhere, light to gentle winds are expected through the forecast period, with a weak surface through extending along 08-09N yielding light S to SW winds to its south. Seas in the 3 to 5 ft range will continue over most of the area. REMAINDER OF THE AREA... The pressure gradient between lower pressure in the vicinity of the ITCZ and collapsing high pressure across NW portions of the discussion area is producing fresh to strong trade winds north of the ITCZ and west of 125W. The aerial extent of the trades will diminish through tonight as the high pressure continues to weaken. Large NW swell is propagating southeastward through the forecast waters, with max seas of around 12 ft in the far western waters N of the ITCZ. This swell will continue to propagate SE across the forecast waters, mixing with waves generating in the Tehuantepec area by early Mon. Seas of 8 ft or greater will cover much of the forecast region W of 108W by tonight. A cold front has crossed 30N140W this afternoon and will sweep SE across the N waters tonight and Mon. Fresh to locally strong N to NE winds will follow the front which is forecast to weaken over NE waters Mon. Cross equatorial SW swell are forecast to reach the southern forecast waters by Tue morning. Marine guidance suggests seas of 8 ft S of 02N between 105W and 120W by early Tue afternoon, and seas of 8-9 ft S of 03N between 96W and 121W by early Tue evening. $$ Stripling