000 AXPZ20 KNHC 200217 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Tue Jun 20 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 0000 UTC surface analysis and satellite imagery through 0215 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends W across the Gulf of Panama, then turns NW through interior Costa Rica to the the Pacific coast of SE Nicaragua at 11.5N86W, continues NW to 13N93W, then turns SW to 09N120W, where scatterometer winds indicate that the ITCZ forms and continues SW to beyond 04N140W. Scattered moderate isolated strong convection is observed along the monsoon trough within 120 nm either side of a line from 06N83W to 09N86W, within 75 nm of 14N93W and 12N102W, along the monsoon trough and ITCZ within 60 nm either side of a line from 11N109W to 08N128W, and N of the ITCZ within 150 nm either side of a line from 11N132W to 07N140W. Broad and elongated surface low pressure is forecast to continue for a couple more days across most of Central America and Eastern Mexico under a diffluent upper ridge, with locally heavy rains expected near the large clusters of TSTMS. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...Only a brief surge of fresh northerly drainage winds will occur across the Gulf of Tehuantepec tonight, with only a moderate N wind forecast on Tue night. Associated seas will build to about 8 ft tonight into Tue. A NW to SE orientated trough across the Baja California Peninsula is amplifying S across the offshore waters to the S of Cabo San Lucas. The trough is forecast to reach a position from 27N114W to 17N114W early Wed, and from 30N116W to 17N120W on Thu with a weak surface low developing along the trough well SW of the offshore waters near 19N120W. The surface low will continue W on Thu night and Fri, dragging the weakening trough that will extend to the N, westward across the offshore waters to the N of 25N through Fri. Large SW swell currently across the offshore waters S of 14N is subsiding from the N, with the forecast for seas less than 8 ft by late Tue. Large NW swell will reach 30N120W on Tue, and spread S across the waters N of 25N seaward of 200 nm on Tue night, with little change then expected through Fri night. These NW swells will subside on Sat. Gulf of California...Moderate SE flow expected across the southern waters on Tue, with these conditions spreading N to along 30N on Wed and Thu. Guidance is hinting at a fresh SE breeze across the gulf waters to the N of 30N late Thu. The pressure gradient will then relax supporting light southerly winds during the weekend. 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 a couple more days. Gentle to moderate SW to W winds are expected across the entire forecast area through Wed, then the pressure gradient will gradually relax with a gentle SW breeze on Wed night and continuing through Sat night. Long period S swell, in the form of 5 to 8 ft seas, currently across the area will subside tonight and Tue, 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 are observed across the tropical waters to the E of 128W, except 3 to 6 ft seas are forecast to the lee of the Galapagos Islands. These seas are already subsiding from the N, and are forecast at 5 to 7 ft by late Thu. A quasi-stationary surface high is centered just N of the area near 34N137W, with moderate anticyclonic flow observed across the discussion area to the W of 120W. An amplifying surface trough extending S-SW from the southern tip of the Baja California Peninsula, is forecast to shift W on Tue, with a surface low developing along the trough near 19N120W on Wed. The low should reach near 18N123W on Fri, then dissipate on Sat. Fresh N winds currently observed across the waters N of 27N between 125W and 132W, are forecast to spread SW across the waters N of 24N W of 120W on Tue and Wed, with large N swell building seas to 8 to 12 ft to the N of 30N W of 120W on Thu. Fresh to locally strong NE winds, with seas of 11 to 13 ft, are expected W of a surface trough dipping into the far N waters on Fri night along a line from 32N128W to 29N131W. The trough and an associated low pressure center will shift W on Sat with the winds diminishing to a gentle N breeze. $$ Nelson