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Tropical weather discussion
NWS TPC/National Hurricane Center Miami FL
0405 UTC Sat Nov 21 2009
Tropical weather discussion for the eastern Pacific Ocean from
the Equator to 32n...east of 140w.
Based on 0000 UTC surface analysis and satellite imagery through
0215 UTC.
...ITCZ...
the ITCZ axis extends from 05n76w to 04n83w to 06n89w to 08n120w
to 07n140w. Scattered moderate to isolated strong convection
within 240 nm N of axis and 90 nm S of axis W of 118w.
...Discussion...
W of 115w...a deep layer trough extending from just inland along
the coasts of Washington-Oregon-N cal to 34n121w continued to
dig E-se on the east side of Rex block centered on the large
ridge N of Hawaii. An associated cold front extends from central
California to 30n128w to 28n40w and continues W to W-NW as a
shear axis. The front was shifting E-se into central California
and approaching NE portions of the forecast area. A 1020 mb high
near 27n132w has collapsed...with the stronger central Pacific
Ridge...centered on a 1027 mb surface high along 34n and N of
Hawaii...was sliding and building ewd behind the cold front.
Morning scatterometer passes showed moderate to fresh 20-25 kt
trade winds S of the high pres from generally 20-22n to the nrn
fringes of the ITCZ along 07.5n from 114w wwd beyond 140w. The
resultant wind waves were mixing with a fading pulse of NW swell
to produce seas of 8 to 11 ft N of 10n and W of 115w...with seas
up 12 to 14 ft from 17n138w downwind...in the strongest NE trade
wind flow. Farther E...the trade wind flow has diminished
slightly from yesterday as the high to the north has collapsed.
These fresh trades to the W will expand and spread farther E
during the next 24-36 hours as the central Pacific high
continues to build E behind the front N of the area. The front
itself is expected to become diffuse by Sat night across NE
portions of the area as the associated upper dynamics lift out.
Meanwhile divergent flow aloft on the right rear entrance area
of a weak jet Max on the se side of the upper trough is
interacting with the modest trade wind convergence to enhance
scattered convection N of the ITCZ W of 118w. Looking ahead the
weekend...the blocking ridge N of Hawaii will break down ahead
of an approaching central Pacific trough. This will allow the
surface ridge that has begun to build behind the current
weakening W coast cold front to remain in place N of the
area...maintaining a broad swath of fresh to strong trades from
10n to 25n W of 120w. Se cross-equatorial flow will converge
with the NE trades to keep clusters of convection active along
the ITCZ W of 120w as well. Meanwhile another pulse of NW swell
yielding combined seas of 10 ft and greater will dominate most
of the marine area W of 115w tonight through Sat.
E of 115w...the main weather phenomena remains the persistent
Central America gap winds. Morning high resolution scatterometer
data showed nely winds of 20 to 25 kt through the Gulf of
papagayo...enhanced by drainage effects... with 20 kt winds
noted off of the Gulf of fonseca. Both of these area are
expected to continue with 20 kt offshore gap winds...but are
likely to diminish slightly during the daylight hours. Fresh
trade winds were pushing from the SW Caribbean S across Panama
as well...through the Gulf of Panama to the ITCZ off the
Colombian coast...but are expected to diminish below 20 kt
within 24 hours. Morning scatterometer data also showed nly flow
of 20-25 kt persisting to flow S out through the Gulf of
Tehuantepec...but is forecast to diminish briefly tonight before
Post frontal winds across the W Gulf of Mexico flow begin to
drain through the pass again late Saturday.
$$
Stripling
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