000 AXPZ20 KNHC 272153 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Mon Sep 27 2021 Tropical Weather Discussion for the eastern Pacific Ocean from 03.4S to 30N, east of 120W including the Gulf of California, and from the Equator to 30N, between 120W and 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. ...TROPICAL WAVES... A tropical wave has its axis along 105W, from 03N to 15N. It is moving westward at 10 to 15 kt. This wave is moving through a very moist environment. Scattered moderate to isolated strong convection is noted within 180 nm east of the wave from 09N- 10N. Scattered moderate convection is within 240 nm east of the wave from 11N to 15N. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...Updated The monsoon trough extends from 10N85W to a 1010 mb low pressure near 10N86W to 13N100W to a 1011 mb low pressure near 12N115W to a 1010 mb low pressure near 12N128W 1010 and to 11N137W. Latest scatterometer data indicates that the ITCZ begins at 09N137W and continues to beyond 09N140W. Aside from convection associated to the tropical wave along 105W, scattered moderate to isolated strong convection is south of the trough from 04N to 08N between 82W-86W, and within 60 nm south of the trough between 117W-120W. Scattered moderate convection is within 60 nm north of the trough between 121W-124W and within 60 nm south of the trough between 127W-129W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... The earlier fresh north to northeast winds across the Gulf of Tehuantepec have diminished to mainly moderate speeds. These winds will become gentle southwest to west winds during afternoon and night time hours through the end of the week and light and variable during the day time. Associated seas across the area are in the range of 5-7 ft. Fresh northerly winds are over the waters west of the Baja California peninsula. light south to southwest winds are over the northern portion of the Gulf of California. Light to gentle winds are noted elsewhere. Seas are 4-7 ft across these open waters, and 2-4 ft in the Gulf of California. Mainly moderate northwest to north winds will prevail west of Baja California, pulsing to fresh during the afternoon through evening hours. The light south to southwest winds over the northern Gulf of California will increase to fresh speeds late tonight through mid-week in advance of an approaching cold front. Otherwise, gentle to moderate winds will prevail through Tue. Large northwest swell will impact the waters west of Baja California by late Tue as the aforementioned cold front begins to weaken and eventually dissipate while moving southward across the region. In reference to the tropical wave along 105W, environmental conditions may become conducive for some gradual development to occur from this system during the next several days, and a tropical depression could form during the latter part of the week well offshore of the coast of mainland Mexico. Movement of this system, if it forms, would be slowly northwestward or northward well offshore of the coast of mainland Mexico. Stay tuned to future marine forecasts that will include detailed wind and wave height information on this possible system. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... Moderate to fresh offshore winds prevail across and downwind of the Papagayo region, with light to gentle winds elsewhere north of the monsoon trough. Gentle to moderate west to southwest winds are south of the monsoon trough. Seas are in the 4-6 ft range from offshore of Colombia northward and offshore of Ecuador in southwest swell. Moderate to fresh offshore winds will pulse each night across the Papagayo region through Wed, then possibly thereafter if low pressure forms west of Central America. Otherwise, light to gentle winds will prevail north of the monsoon trough, with mainly moderate winds south of the monsoon trough. Cross- equatorial southwest swell will continue to propagate through the regional waters through the rest of the week, with peak seas reaching about 6 ft. REMAINDER OF THE AREA... A surface trough extends from near 23N133W to 18N135W. Generally, moderate northeast winds are present northwest of the trough, where seas are peaking to 7 ft. Broad and weak ridging along with gentle to moderate trades dominate the remainder of the open waters north of the convergence zone and west of about 118W. Gentle to moderate southerly winds prevail south of the convergence zone, except between 112W-120W and between 127W-133W where both ASCAT data from last night and this afternoon revealed fresh to strong southwest winds due to a stronger gradient present induced by the 1011 mb low near 11N115W. Seas are in the 5-7 ft range north of 11N, and 6 to 7 ft south of 11N, except higher seas of 8-9 ft are found between 105W-121W as were noted by an altimeter pass. These seas are mainly attributed to the fresh to strong southwest winds near the aforementioned 1011 mb and 1010 mb lows, respectively. The surface trough will gradually become diffuse as it shifts to near 140W Tue. A cold front that is just northwest of the area will begin to move across the far northwest waters tonight, reach from near 30N132W to 28N140W early Tue and from near 30N118W to 26N140W by early Wed as it begins to dissipate. The front is forecast to gradually dissipate near 21N by the end of the week as a a large area of high pressure builds across the area. The associated gradient will act to freshen the winds west of 118W. A set of long-period northwest swell following in the wake of this front is expected to build seas to the range of 8-11 ft to the west of 120W, spreading southward through the end of the week while decaying. The highest of these seas is expected to be over the far northeast waters. $$ Aguirre