000 AXPZ20 KNHC 090330 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Thu Nov 09 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 0300 UTC. ...SPECIAL FEATURES... A tight pressure gradient has set up over southeastern Mexico, and is bringing strong northerly winds through the Isthmus of Tehuantepec and across the Gulf of Tehuantepec where sea surface temperatures are quite warm, 29.5 to 30.5 Deg. Celsius. These conditions are expected to continue into Thursday morning. High pressure surging southward behind a cold front moving across the western Gulf of Mexico will push a cooler air mass towards the eastern slopes of the Sierra Oriental mountains along eastern Mexico that will act to further tighten the pressure gradient already in place allowing for these winds to increase to gale force by early Thursday afternoon. A gale warning is already in effect for the Gulf of Tehuantepec through 48 hours, and most likely will have to extend beyond the 48 hour forecast period of the discussion. Seas are expected to build to the range of about 10-15 ft with these gale conditions. Model guidance suggests that this event will last through the next few days, while pulsing down to just below gale force in the late mornings. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N85W to 10N100W to 08N110W to low pressure near 10N122W 1009 mb to 10N138W where scatterometer winds from this afternoon indicate the ITCZ then begins and continues to beyond 08N140W. Scattered moderate convection is within 90 nm S of the axis between 83W-86W, within 120 nm N of the axis between 102W-108W and also within 60 nm N of the axis between 117W-119W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A ridge will dominate the waters W of Baja California through the rest of the week, while a trough will meander between the coast of NW Mexico and the Gulf of California. Moderate to locally fresh NW to N flow will prevail across the waters W of Baja California, increasing to fresh to locally strong offshore of the northern waters Thu night through Fri. A cold front is expected to weaken before reaching the area on Friday, but the associated long-period NW swell inducing seas in the range of 8- 10 ft will propagate southeastward across the waters N of 23N and to the W of Baja California on Friday, then spread southward through all the waters W of Baja on Saturday while subsiding slightly. A relatively strong jet stream branch from the central Pacific waters is advecting abundant moisture ENE towards northern and central Baja California and far southern California. This moisture consists of multilayer clouds with possible isolated showers and thunderstorms underneath them. Gulf of California: The pressure gradient will tighten a little resulting in a narrow swath of fresh to locally strong NW winds from 25N to 28N by this afternoon. The pressure gradient will relax with moderate NW flow only to the S of 26N by Thursday evening. Mainly light and variable winds and seas of 2 ft or less will then prevail for the end of the week into the upcoming weekend. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: moderate NE winds will pulse during the overnight hours tonight, with seas building to 5 or 6 ft downstream of the Gulf near 11N87W. Light and variable winds and 4 to 6 ft seas, are expected elsewhere to the N of 09N, while moderate to locally fresh southerly winds and 5 to 7 ft seas, are forecast S of 09N through the remainder of the week and the upcoming weekend. REMAINDER OF THE AREA... A 1020 mb high pressure system is analyzed near 26N132W and extends a ridge southeastward to near 23N119W and westward to near 26N139W. This high center is forecast to remain nearly stationary through Thursday morning, then track northeastward to near 29N124W by Thursday evening. A low-level trough is roughly along 134W from 11N to 18N. Scattered moderate convection is seen within 60 nm E and within 180 nm W of the trough from 13N to 18N as it is being enhanced by a nearly stationary upper level low at 15N139W. A 1009 mb low pressure system remains embedded within the monsoon trough near 10N122W. An Ascat pass from 1758Z Wednesday afternoon highlighted winds of 20 kt within 120 nm of the low in the NE quadrant, and within 60 nm of the low in the SE quadrant. Latest satellite imagery shows that the earlier observed scattered moderate isolated strong convection that was within 60 nm NW and SE quadrants of the low has significantly diminished. Only scattered moderate convection remains within 60 nm of the low in the NW quadrant. The low is forecast to move generally westward to near 10N127W by early Thursday evening and to near 12N131W by early Friday evening. A cold front has moved into the far NW corner of the forecast area. The main issue with this front will related to its impacts on waveheights. It is followed by a new set of long period NW swell. The front will reach from near 32N138W to 28N132W, and as a weakening stationary front to 27N140W by early Thursday evening, then quickly begin to dissipate as high pressure behind it overtakes it near a position from 32N116W to 28N125W and dissipating stationary from there to 26N140W by late Friday afternoon into Friday evening. The associated long period NW swell, with seas of 8 to 13 ft seas will propagate southeastward through the northern forecast waters while decaying. Seas of 8 ft or greater will cover the waters N of 15N W of 115W by Friday evening, then begin to subside to near 8 ft throughout the waters by Sunday evening. A pretty strong jet stream branch extends from the deep tropics of the central Pacific northeastward towards the NE portion of the area. Latest satellite imagery shows broken to overcast multilayer clouds along and S of the jetstream branch roughly within 90 nm either side of a line from 19N134W to 25N125W to 29N120W, and well NE from there towards northern Baja California and southern California as mentioned above. Upper disturbances riding northeastward along this jet stream are helping to enhance the aforementioned cloudiness as well as trigger off small pockets of isolated showers and thunderstorms. This jetstream branch set up is forecast to change little over the next 24-48 hours. $$ Aguirre