000 AXPZ20 KNHC 020242 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Sat Sep 2 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. ...SPECIAL FEATURE... Tropical Storm Lidia is centered near 26.4N 112.9W, or 70 nm SSW of Santa Rosalia Mexico at 8 pm PDT, moving NW at 10 kt, with estimated minimal central pressure of 994 mb. Maximum sustained winds are 45 kt with gusts to 55 kt. Latest satellite imagery shows scattered moderate to strong convection within 60 nm of the center in the E semicircle. Scattered moderate isolated strong convection is elsewhere from 25N to 26N between 1110 and 113W, and just inland Mexico from 26N to 28N. This convection is resulting in very heavy rainfall creating the potential for life- threatening flash floods and mudslides. Moisture associated with this convection is expected to gradually spread northward to the SW United Stated during this weekend. Lidia is forecast by the latest NHC advisory to track to the NW near or along the west coast of the Baja California Peninsula through Sat, then move offshore just to the NE of Punta Eugenia on Saturday afternoon as it weakens to a depression by Saturday evening. It will accelerate to the NW weakening to a remnant low N of 29N on Sun. Please see the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP4/WTPZ24 KNHC for more details, and for the Public Advisory please see the latest NHC forecast/advisory under AWIPS/WMO headers MIATCPEP4/WTPZ34 KNHC. ...TROPICAL WAVES AND TROPICAL LOWS... A tropical wave is analyzed to the N of 08N along 88W, moving westward at 10 to 15 kt. Scattered moderate isolated strong convection that fired up on Friday afternoon over much of the eastern portions of Honduras and Nicaragua has since shifted to the central and western sections of those countries and the immediate adjacent waters. Scattered moderate convection is seen along the coast of northern Panama. A tropical wave is analyzed to the N of 09N along 102W with a 1010 mb surface low along on the wave axis at 13N101W. The system is moving W at 12 kt. Scattered moderate isolated strong convection is observed within 60 nm of a line from 10N107W to 13N104W, and within 30 nm of a line from 16N98W to 16N102W. A nearly stationary 1010 mb surface low is embedded in the monsoon trough at 11.5N136W. Only isolated weak moderate convection is noted within 240 nm of the low in the NE quadrant. ..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from low pressure over NW Colombia to across northern Costa Rica, then W to 11N92W to 12N96W through a low pressure at 13N102W that is along a tropical wave along 102W, where the monsoon trough loses identity in the broad cyclonic circulation associated with Tropical Storm Lidia. Scatterometer data from Friday afternoon indicated that the monsoon trough resumed near 18N120W and extends SW through a 1010 mb surface low at 11.5N136W and to beyond 11N140W. Scattered moderate isolated strong convection is within 180 nm N of the trough between 94W and 96W. Similar convection is occurring over the gap between both monsoon trough segments over an area described from 13N to 17N and between 109W and 117W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Refer to the special features paragraph for information on Tropical Storm Lidia. A ridge will build eastward E along 23N on Sun in the wake of Lidia, with a moderate to locally fresh NW breeze setting up across the open waters W of the Baja California Peninsula, as well as across the Gulf of California through early Mon. Gulf of Tehuantepec: light offshore nocturnal flow expected tonight, then moderate drainage flow is forecast at night for Saturday, Sunday and and Monday. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Gentle to locally moderate offshore nocturnal flow expected tonight and on Sat night, with a moderate to fresh E breeze forecast on Sun night. Otherwise, light and variable flow is expected N of the monsoon trough axis through early next week, while moderate to locally fresh southerly winds are expected to the S of the trough axis. REMAINDER OF THE AREA... Just about the entire area N of 12N between 104W and 126W is dominated by broad cyclonic flow that encompasses Tropical Storm Lidia. Both CIMSS Total Precipitable Water (TPW) imagery animation and water vapor imagery depict abundant deep moisture throughout this area of cyclonic flow, while very dry air aloft is to its NW as seen in the water vapor imagery. The 18 UTC analysis has a ridge extending into the discussion area from 32N140W to near 22N126W. The pressure gradient between it and low pressure near the monsoon trough is allowing for mainly gentle NE winds to exist N of the monsoon trough W of 126W along with seas in 5 to 6 ft range. An area of moderate NE winds is over the NW portion N of about 26N and W of 132W, with seas of 5 to 7 ft. Fresh southerly monsoonal winds, and seas of 5 to 8 ft are observed S of 15N between 100W and 130W primarily in mixed SE and SW cross- equatorial swell. The swell is forecast to begin to dissipate on Sunday allowing for seas to slowly subside into early next week. $$ Aguirre