Area Forecast Discussion
Issued by NWS Tiyan, Guam

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FXPQ50 PGUM 302145 CCA

Area Forecast Discussion...Corrected
National Weather Service Tiyan GU
727 AM ChST Sat Oct 31 2020

Corrected Lat/Lon coordinate for Atsani

.Marianas Synopsis...
Disheveled Tropical Depression Atsani (23W) is centered near 13N140E,
moving west-northwest at 15 miles per hour. A few of Atsani`s
outermost, weak rainbands are sliding through Tinian and Saipan this
morning, but overall shower coverage is isolated. Buoy and altimetry
data indicate combined seas are between 5 and 7 feet with trade
swell from the east and wind waves from the southeast.


Little change to the previous forecast other than to reduce cloud
cover for today and tonight based on satellite imagery. Southeast
winds will ease through the day as Atsani pushes farther away from
the Marianas. Although a few thunderstorms popped up east of Saipan
this morning, expect this band to wane and lift north of the coastal
waters by mid-morning. Overall, pleasant weather is expected the
next few days with drier trade winds establishing later today and
Sunday. Overnight Monday into Tuesday morning could feature a slight
uptick in showers as a very subtle wrinkle in the trade flow moves
through along with an upper-level trough.

A notable increase in clouds, showers and trade winds is still on
track for the second half of the coming week as a disturbance
approaches from eastern Micronesia. GFS and ECMWF show variations of
the same theme but will need to refine timing.


Made a few adjustments to the wave grids based on Atsani`s quick
departure and lack of intensification. Latest guidance and current
trends suggest only meager west swell will reach the Marianas this
coming week. Combined seas of 5 to 7 feet will subside a notch
tonight and Sunday. Seas and winds rise again the middle of next week
as stronger trade winds push in with a disturbance.


.Tropical systems...
Tropical Depression Atsani (23W) will continue to lift towards the
west-northwest the next few days with only slight intensification.
Micronesia is no longer expected to experience any direct effects
from Atsani.

A disturbance in eastern Micronesia dubbed Invest 91W will trek
westward in the coming days. Overall model consensus is that this
system will remain broad and disorganized as it moves through the


.Eastern Micronesia...
The main weather feature in the east this morning is a large trade-
wind disturbance stretching from Kosrae across Kwajalein and Majuro
nearly to the date line. As it tracks westward, it will bring
scattered showers and thunderstorms to Majuro today, to Kosrae today
through Sunday, and to Pohnpei late tonight through Sunday night.
Once it moves past Pohnpei, weather looks quiet Mon-Wed for all
locations except Kosrae, where a new disturbance develops west of
Majuro in time to bring wet weather to Kosrae on Wednesday.
Background seas will generally be 4 to 5 feet, but the passage of
the disturbance will build combined seas to as high as 6 feet at
Majuro today, 8 feet at Kosrae on Sunday, and 7 feet at Pohnpei
Sunday and Sunday night.


.Western Micronesia...
An active pattern is in place across western Micronesia with west to
southwest flow across Palau and Yap that involves TD Atsani (23W)
north of Yap. These moist southwest winds are expected to bring
scattered showers and isolated thunderstorms to Yap today through
Sunday, and to Palau tonight and Sunday and again Tuesday and
Wednesday as a new disturbance takes shape. Chuuk looks fairly dry
through the weekend, but by Tuesday the disturbance tracking through
eastern Micronesia reaches Chuuk with scattered showers and isolated
thunderstorms that should persist into Wednesday. Throughout the
next five days, combined seas should range between 3 and 5 feet at
all three locations.


Marianas Waters...None.


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