000 AXPZ20 KNHC 211545 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1545 UTC Sat Oct 21 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 1200 UTC surface analysis and satellite imagery through 1800 UTC. ...TROPICAL WAVES... The axis of a tropical wave is near 89W north of 09N. Earlier convection associated with this tropical wave was likely also influenced by overnight coastal effects, and has since dissipated. The axis of a tropical wave is near 97W N of 08N, moving W at 10 to 15 kt. No significant convection is noted. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 08N82W to 09N120W, where it transitions to an intertropical convergence zone and continues west to beyond 10N140W. Scattered moderate convection is noted from 07N to 19N between 95W and 105W. Scattered moderate to isolated strong convection is noted from 07N to 10N between 112W and 117W, and from 08N to 10N between 135W and 140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... The main forecast issue will be strong gales in the Gulf of Tehuantepec next week. Fresh winds will pulse overnight tonight through the Gulf of Tehuantepec, related to local drainage effects. The pressure gradient will tighten starting late Sunday, as a cold front moves through the western Gulf of Mexico Sunday night ahead of the northern portion of a tropical wave moving across northern Central America and the Yucatan peninsula. These factors, along with cool, dry air behind the front reinforcing already present local drainage effects will allow strong to minimal gale winds starting Monday morning through the Gulf of Tehuantepec. The gradient will tighten further as high pressure behind the settles over the southern plains, northeastern Mexico and the western Gulf of Mexico through late Monday, allowing for stronger gales by early Tuesday persisting through mid week. Seas will build as the gale conditions continue, reaching 12 ft Monday, and in excess of 15 ft by late Wednesday. The shorter period northerly swell resulting from the strong gap winds will propagate well to the south of Tehuantepec, mixing with longer period northwesterly and southerly swell through mid week. Farther north, strong northwest to north winds are ongoing off the coast of Baja California north of Cabo San Lazaro between strong high pressure west of the area and troughing over the southwest United States and north central Mexico. These winds will diminish as the troughing weakens. Seas will are peaking near 18 ft off the northernmost coast of Baja California Norte in northerly swell and are expected to subside through early next week as winds diminish and the swell decays. The swell will propagate SE, with seas 8 ft or greater covering all of the offshore forecast zones W of Baja California through the weekend before subsiding below 8 ft the middle of next week. High pressure building over the Great Basin region of the western United States will cause NW winds to strengthen over the Gulf of California through Tuesday, diminishing thereafter as the gradient weakens. Winds will be strongest on Sunday night through Monday when seas peak around 8 ft. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gentle to moderate winds will prevail over the forecast area the next several days. NW swell originating from the Gulf of Tehuantepec will propagate into the offshore waters of Guatemala and El Salvador by the middle of next week. REMAINDER OF THE AREA... A set of large NW swell with seas near 15 ft will continue to propagate SE while gradually subsiding into early next week. Seas will subside to less than 12 ft Sunday afternoon. Seas associated to this swell are expected to further subside, to less than 8 ft, by midweek. $$ Christensen