497 axpz20 knhc 071000 twdep

Tropical weather discussion  
NWS TPC/National Hurricane Center Miami FL
1005 UTC Sat Nov 07 2009
Tropical weather discussion for the eastern Pacific Ocean from 
the Equator to 32n...east of 140w. 
Based on 0600 UTC surface analysis and satellite imagery through 
0815 UTC.
...Tropical lows...
Low pres centered near 12n91w estimated at 1006 mb and is now 
moving N slowly in response to the upper trough immediately to 
its W which is also contributing both southwesterly wind shear 
and dry air which is being entrained by the low. The system is 
expected to dissipate to a trough over the next 24 hours within 
this hostile environment. Currently...scattered moderate with 
isolated strong convection is displaced from the low level 
center...between 60 nm and 180 nm in the NE quadrant of the low. 
Two ship reports in the eastern semicircle of the low reported 
winds in the 25 to 30 kt range at 0600 UTC...but these winds 
should rapidly diminish today as the low weakens.
Low pres centered near 12n116w is estimated at 1010 mb. The 
surface low is under an upper anticyclone...and the associated 
upper diffluence has been enhancing convection. Scattered 
moderate with isolated strong convection lies within 180 nm NW 
and se quadrants of the low. This low is expected to weaken over 
the next 24-36 hours as the upper jet to its N sinks 
southward...providing 30 to 40 kt of shear over the system. 
...ITCZ...
The ITCZ axis extends along 07n77w to 11n87w to 07n97w to 
12n115w to 08n140w. Scattered moderate convection can be found 
near Panama within 60 nm N and 120 nm S of the ITCZ axis between 
78w and 82w. Scattered moderate to strong convection lies within 
90 nm S of the ITCZ axis between 98w and 101w.
...Discussion...
N of 20n...
an upper level anticyclone is centered near 08n113w with a ridge 
axis extending NE to Manzanillo...Mexico and continuing N into 
Texas. An upper low lies over the northern Gulf of California 
near 29n113w and is approaching this ridge axis from the W. The 
tropical moisture plume that extended from the ITCZ region to 
the eastern edge of this upper low this time yesterday has been 
cut off. Only high clouds remain...primarily over the northern 
half of the Gulf of California as well as over NW Mainland 
Mexico. This upper low will continue E away from the forecast 
area over the next few days. There is little indication of the 
upper low at the surface where a high pres ridge stemming from a 
1032 mb high near 36n152w dominates the remainder of north 
waters. The pres gradient between this high and low pres over 
the Gulf of California has brought 20 kt northerly winds off the 
W coast of Baja California. These winds should dissipate over 
the next few hours as a cold front bears down on the high pres 
system from the NW and weakens the ridging. While this front is 
expected to dissipate before it can reach forecast waters...long 
period NW swell from the system is already beginning to push 
into NW waters with significant wave heights increasing to 18 ft 
over NW water this morning. Highest seas will shift E quickly 
today across N waters...with the leading edge of the swell train 
progressing se. 
S of 20n...
aside from the low pres systems described above and The Gap 
winds described below...easterly trade winds are the dominant 
feature of note. 20 to 25 kt trades are currently limited to 
between 10n and 20n W of 127w...with a small area of 20 to 25 kt 
winds associated with the low pres system near 12n116w. The area 
of strongest trade winds will shift S in response to the 
aforementioned reorganization of the high pres system to the 
north. Another weak low pres system lies near 10n108w. According 
to the 0504 ascat pass...the low has a small area of 20 to 25 kt 
winds within 90 nm in its N quadrant. Scattered moderate 
convection can currently be found within 90 nm NW and 60 
nm se semicircles of the low which now lies under the 
anticyclone in a favorable area for convection. Conditions 
should become more hostile for the system over the next day or 
two...and this low is expected to dissipate with little fanfare.
Gap winds...
a partial ascat pass from 0324 UTC showed winds in the 30 to 33 
kt range in the Gulf of Tehuantepec. Considering the pass 
omitted a portion of the area believed to have the strongest 
winds and the fact that ascat generally runs low with winds near 
gale force and higher...there is likely still a gale here that 
will continue through the morning hours. However...there is a 
considerable amount of uncertainty with the forecast for the 
strength and position of low pres in the Bay of Campeche...the 
persistent low pres near 12n91w that is now drifting N...and 
Tropical Storm Ida now over the eastern Gulf of Honduras and 
forecast to move northward and strengthen. All of these factors 
will influence the wind...or lack of wind...in the Gulf of 
Tehuantepec over the next few days. Depending on the orientation 
of the low pres centers N of the area...another N surge may 
occur as early as sun in the Gulf of Tehuantepec. 
$$
Schauer







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