000 AXPZ20 KNHC 182149 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sun Jun 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 1800 UTC surface analysis and satellite imagery through 2145 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends NW across interior Costa Rica to the the Pacific coast of Nicaragua at 12N87W, and continues NW through an embedded 1007 mb surface low pressure at 13N91W, then turns SW to 10N128W where scatterometer winds indicate that the ITCZ forms and continues SW to beyond 08N140W. Scattered moderate isolated strong convection is observed within 75 nm of 07N79W, within 90 nm of 08N87W, and across the E Pacific to the N of 07.5N between 89W and 97W, and along the monsoon trough and ITCZ within 120 nm either side of a line from 12N100W to to 08N119W to 11N131W. Broad surface low pressure is forecast to continue for the next few days across most of Central America and Eastern Mexico under a diffluent upper ridge. Additionally, a surface low centered near the E coast of the Yucatan Peninsula is forecast to move slowly NW across the Yucatan Peninsula through tonight, and then track over the S-Central Gulf of Mexico on Mon and Tue and likely strengthen. Locally heavy rains are expected near large clusters of TSTMS over portions of Central America and eastern Mexico during the next several days. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...Fresh to locally strong northerly drainage winds are expected across the Gulf of Tehuantepec on Mon and Tue nights. A NW to SE orientated trough across the Baja California Peninsula is expected to amplify S across the offshore waters to the S of Cabo San Lucas through Mon while drifting W, reaching a position from 27N114W to 17N114W early Wed. A surface low will begin to develop along the trough near 19N115W on Tue night, and move W of the offshore waters to near 17N118W on Wed night. As the low moves westward, it will drag a weakening trough W across the offshore waters to the N of 25N on Thu and Fri. Large SW swell currently across the offshore waters S of 13N will spread N to along 17N late tonight, and then begin to subside on Mon with seas less than 8 ft by early Wed. Large NW swell will reach 30N120W on Tue, and spread S to along 25N on Tue night, with little change then expected through Fri night. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Broad low pressure is forecast across Central America and the adjacent offshore waters for the next few days. A moderate to locally fresh SW to W breeze is expected across the entire forecast area through Mon morning, then the pressure gradient will relax with a gentle to moderate SW to W breeze forecast through Fri night. Long period SW swell in the form of 6 to 9 ft seas currently across the area, will begin to subside on Mon with seas less than 8 ft everywhere by Wed afternoon. REMAINDER OF THE AREA... An area of 6 to 9 ft seas, primarily due to SW swell, will affect the waters S of 16N E of 132W. Expect 3 to 6 ft seas to the lee of the Galapagos Islands. These seas will begin to subside from the N on Mon, and continue to subside through Fri night. A quasi-stationary surface high is centered just N of the area near 34N136W with a ridge extending S-SE to near 11N123W. This ridge will gradually shift westward over the next few days and reach a position W of 140W by mid week. An amplyfying surface trough extending S from the southern tip of the Baja California Peninsula is forecast shift W on Tue, with a surface low developing along the trough near 17N118W on Wed. The low should reach near 16N123W on Fri. This will result in the pressure gradient tightening across the subtropics this week, with fresh N winds developing across the waters N of 29N between 125W and 132W on Mon. These fresh N-NE winds will spread SW across the waters N of 25N W of 120W on Tue and Wed, with large N swell building seas to 8 to 12 Ft to the N of 20N W of 120W on Thu. Strong n winds with seas of 11 to 13 ft are expected N of 30.5N between 124W and 138W on Thu and Fri. $$ Nelson