Tropical Weather Discussion

axpz20 knhc 211005

Tropical weather discussion 
NWS National Hurricane Center Miami FL 
1005 UTC Wed Sep 20 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 0600 UTC surface analysis and satellite imagery through 
0900 UTC.

...Special features...

A 1010 mb low pressure center is near 15n96w. Precipitation: 
scattered to numerous strong within 180 nm N of trough between 
99w and 105w. Global models suggest that the elongated trough 
will persist offshore of the coast in this region, and that 
environmental conditions are favorable for development into a 
tropical cyclone during the next few days. Environmental 
conditions are expected to be conducive for gradual development. 
It is likely that a tropical depression may form in two to three 
days, as the system moves slowly toward the west-northwest. 
Heavy rains are expected in parts of southern Mexico during the 
next several days. The chance of formation is medium.

...Tropical waves...

A tropical wave is along 88w/89w from 17n southward. It is 
possible that this may be in the process of being absorbed in a 
broad and elongated trough, that extends across the waters of 
southeastern Mexico. Precipitation: scattered moderate to 
isolated strong from 08n to 13n between 85w and the tropical 

..intertropical convergence zone/monsoon trough...         

Monsoon trough from 09n79w to 11n86w to low pres near 15n96w 
1010 mb to 16n102w to 13n116w to 11n122w to 11n130w to low pres 
near 12n136w 1012 mb to 13n140w. Scattered to numerous strong 
within 180 nm N of trough between 99w and 105w. Precipitation: 
scattered moderate isolated strong within 270 nm S of trough E 
of 94w... within 210 nm S of trough between 105w and 
116w...within 180 nm S of trough between 120w and 123w...within 
90 nm S of trough between 128w and 129w... and within 240 nm S 
of trough W of 131w.


Offshore waters within 250 nm of Mexico...  

A surface ridge passes through 32n140w to 28n132w to 22n126w.
Low pressure in southern Arizona, and an approaching cold front 
that is pushing southward along the coast of central California, 
will induce fresh to strong SW winds in the northern part of the 
Gulf of California tonight through early Fri morning. Maximum 
sea heights will be building to 5-7 ft north of 30n. The local 
effects will be less evident to the west of Baja California, and 
to the south of 29n in the Gulf of California, until Fri night 
when winds will freshen from N to S along the Pacific coast of 
baja. The possible development of low pressure along the coastal 
waters of southern Mexico Thursday through the weekend will 
increase the wind speeds and the sea heights to the south of the 
coast of Mexico between 97w and 105w. 

Offshore waters within 250 nm of Central America, Colombia, and 
within 750 nm of Ecuador...

A fairly active monsoon trough along the coast of Central 
America from Guatemala to Panama will maintain active convection 
across the coastal waters during the next few days. Expect SW 
winds south of the trough to strengthen gradually to 20-25 knots 
from 24 hours to 48 hours into the forecast period. The winds 
will become more westerly by Friday. Further south, gentle to 
moderate southerly winds are expected to persist south of 05n 
through the weekend. S to SW swell continues to propagate across 
the area with seas in the 5 to 6 foot range east of 100w.

Remainder of the area...

The Post-tropical remnant low of Norma 1009 mb is near 22n117w.
It is a well defined swirl of low and mid level clouds and 
stratiform precipitation. Winds are estimated to be 20-25 kt 
within 120 nm of the center in the W semicircle, and seas to 8 
ft. The low will move slowly NW and weaken through Friday.

The Post-tropical remnant 1012 mb low of Otis is near 16n132w.
It remains a swirl of low level clouds and limited stratiform 
precipitation. Fresh to strong N-NE winds and 8-9 ft seas are 
with 150 nm NW of the low center. The low is expected to move SW 
and weaken into a trough through Friday, with seas gradually 
diminishing to 6-7 ft.

NW swell associated with strong N-NW winds north of the area is 
producing combined seas of 8-10 ft north of a line from N of 
line from 30n117w to 25n120w to 18n130w to 18n140w.
This area of NW seas is expected to contract and shift slightly 
eastward through Thu night. Another weaker round of NW swell 
associated with a cold front west of California is expected to 
arrive Fri night. High pressure centered well N of the area and 
lower pressure associated with the convergence zone will 
maintain moderate trade winds across most of the remainder of 
the area through the weekend. 



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