831 AXPZ20 KNHC 171557 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1556 UTC Tue Jul 17 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 1200 UTC surface analysis and satellite imagery through 1530 UTC. ...TROPICAL WAVES... A tropical wave is analyzed N of 05N along 90W and is estimated to be progressing W at 12 kt. No significant convection is observed with this wave. A tropical wave is analyzed from 04N to 14N near 109W. Scattered moderate convection is noted where the tropical wave intersects the ITCZ from 07N to 09N between 108W and 110W. A tropical wave is analyzed from 08N123W through a 1009 mb surface low embedded along the wave at 14N122W to 17N121W. This system is moving W at 10 to 15 kt. Scattered moderate and isolated strong convection is observed from 14N to 17N between 119W to 121W. Earlier scatterometer passes showed fresh easterly flow within 180 nm either side of the wave axis from 13N to 15N. A concurrent altimeter satellite pass showed seas to 8 ft. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N78W to 08N100W. The ITCZ continues from 08N100W to the tropical wave near 109W, then on to 10N116W. The ITCZ continues from the 1009 mb low pressure near 14N122W to 09N130W to 10N140W. Scattered moderate convection is noted within 120 nm either side of the ITCZ west of 125W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A scatterometer pass from the previous evening along with reports from Salina Cruz on the coast of Mexico near the Gulf of Tehuantepec indicated fresh to strong drainage flow into the Gulf of Tehuantepec earlier this morning. This flow is being enhanced between high pressure over the western Gulf of Mexico and a tropical wave passing westward south of the region, and strong nocturnal winds with seas to 7 ft are expected into Thu morning. Light to gentle breezes and minimal seas are noted elsewhere over Mexican offshore waters. Divergent flow aloft associated with a mid to upper low over northwest Mexico is supporting scattered overnight showers and thunderstorms inland over the mountainous terrain east of the Gulf of California. Some of this activity is currently impacting the southern Gulf of California. This may repeat again tonight, but taper off early as the mid/upper low migrates through the region. Looking ahead, long period southwest swell will propagate into the Mexican offshore waters by Fri, with combined seas in open waters building in excess of 5 ft. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Strong nocturnal drainage flow, accompanied by 6 to 8 ft seas, are expected through Thu night with extended guidance suggesting these conditions will resume on Sun night. Gentle to occasionally moderate E winds are forecast elsewhere N of the monsoon trough which is meandering between 07N and 10N. Moderate southerly winds are forecast S of the monsoon trough for the next several days accompanied by 4 to 6 ft seas. Long period southerly swell, in the form of 7 to 8 ft seas, will pass north of the Equator by Thu, and propagate northward into the offshore waters of Central America through Sat. REMAINDER OF THE AREA... A broad upper low is centered near 21N127W, supporting an associated 1009 mb surface low near 14N122W along a tropical wave. While upper winds are unfavorable for further development, scatterometer data confirms fresh to occasionally strong easterly flow in a swath on the northern side of the surface low through, with seas observed at 8 ft. The tropical wave will continue west, reaching 130W by Thu, with the low gradually dampening out as the upper lift north of the area, allowing winds and seas to diminish. The subtropical ridge will build north of 20N, supporting moderate to fresh trade winds from 08N to 15N west of 130W by late week. Long period cross-equatorial swell, in the form of 7-9 ft seas, will move across the Equator between 90W and 125W on Wed, and continue to propagate N across the discussion area through Sat. $$ Christensen