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Tropical Weather Discussion

Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Thu Aug 17 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 1545 UTC. ...SPECIAL FEATURE... A surface low is analyzed at 12N111W and is estimated at 1008 mb, and has moved W at 10 kt over the past 24 hours. Strong E to SE winds, and 7 to 9 ft seas are observed within 90 nm NE of the low. Scattered moderate to strong convection is currently observed within 180 nm over the W semicircle of the low. Environmental conditions are favorable for tropical cyclone formation as this low moves northwestward to near 15.5N116.5W early Fri, and near 16.5N122W early Sat. Refer to High Seas Forecast under WMO/AWIPS headers FZPN03 KNHC/MIAHSFEP2 for additional information. ..TROPICAL WAVES AND TROPICAL LOWS... A tropical wave is analyzed to the N of 06N along 90W. Isolated strong convection is observed to the S of 12N within 60 nm of the wave axis. This wave has been progressing W at about 20 kts over the past 24 hours, but is expected to slow it's forward speed over the the next few days. A tropical wave is analyzed from 08N104W to 20N107W and has moved W at 15 kt over the past 72 hours. Scattered moderate and isolated strong convection is observed to the N of 17N within 150 nm of the wave axis, and to the S of 12N within 90 nm W of the wave. A 1009 mb surface low is analyzed N of the monsoon trough at 16.5N121W. Fresh E to SE winds are observed within 360 nm over the N semicircle of the low with seas of 6 to 7 ft. The low is forecast to move w and weaken into to open trough by early Sat. The remnants of former tropical cyclone Jova continue to spin near 18N135W with a pressure of about 1009 mb. Only weak showers are indicated within about 150 nm over the NE semicircle. The pressure gradient is supporting moderate to locally fresh N to NE winds and 6 to 7 ft seas within 330 nm over the NW quadrant of the low. The low is forecast to move W-SW and weaken to an open trough by early Fri. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends WSW across the far SW Caribbean from 09N76W to across the Gulf of Panama to the Pacific coast of Costa Rica at 08N83W to a tropical wave at 09N90W TO 07N95W, then turns NW trough a second tropical wave at 13N106W, then turns SW through a surface low embedded in the monsoon trough at 12N111W, then turns WNW to 15N129W, then SW to beyond 13N140W. Except as previously mentioned, scattered moderate isolated strong convection is noted within 90 nm either side of a lines from 09N84W to 09N88W and from 06N92W to 09N98W, and within 150 nm either side of a line from 13.5N116W to 12N140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A NW to SE orientated low level trough will meander E to W across the Baja California Peninsula and Gulf of California through Mon night with a surface low developing intermittently along the trough over the far northern Gulf of California waters. Currently the low has a surface pressure estimated at 1008 mb resulting in moderate westerly winds along 30N. A NW to SE orientated ridge extends across the offshore waters from 23N116W to 21N107W. A gentle NW breeze is expected today to the W of the Baja California Peninsula, except a moderate NW breeze forecast within 90 nm of the Baja coast, with combined seas of 3-5 ft. Guidance still suggests that the pressure gradient will tighten each evening with moderate NW flow W of Baja, except fresh NW flow within 90 nm of the Baja coast with 3 to 6 ft seas. Gulf of California...light to gentle southerly flow will persist across the Gulf of California through the upcoming Mon night, except a moderate to locally fresh breeze will surround the low pressure center over the waters N of 29.5N. Gulf of Tehuantepec: strong N drainage winds are forecast during the overnight hours with seas building to 9 ft downstream of the Gulf waters near 15N95W. Guidance is hinting at near gale force drainage flow on Mon night. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: fresh to locally strong ENE winds are expected tonight, then the pressure gradient will relax supporting moderate nocturnal drainage through Mon morning. Thereafter, fresh E winds may develop on Mon afternoon in association with a low pressure system developing along the monsoon trough near 09N88W. This low, if it does form, should move NW paralleling the coast about 150 NM offshore through the middle of next week. Otherwise, light and variable to gentle NE to E flow expected N of the monsoon trough throughearly Mon, while moderate to locally fresh southerly winds are expected S of the monsoon trough axis with 3 to 6 ft seas throughout. REMAINDER OF THE AREA... The subtropical ridge extends from 32N133W to near 23N116W. Except as previously mentioned in the above paragraphs, moderate to locally fresh anticyclonic flow is forecast N of the monsoon trough and W of 120W. Long period southerly swell, in the form of 6 to 8 ft seas, is observed S of 06N between 105W and 115W. These seas will subside to less than 8 ft by sunset today.