Scientific Forecaster Discussion
fxpq60 pgum 220912
Area forecast discussion
National Weather Service tiyan GU
712 PM chst sun Oct 22 2017
Andersen Air Force Base Doppler weather radar shows widely
scattered showers moving through the marianas waters. The VAD wind
profile indicates north winds just off the surface which turn
toward the northeast aloft. The buoys reveal hazardous seas of 10
to 12 feet in the Guam waters and 12 to 15 feet in the waters of
main player in the forecast is tropical depression 27w. It is
headed away from the marianas now, but it should loop and start
coming back in our direction. Grids currently handle this
scenario, however the details could need anything between minor
tweaks to wholesale overhaul depending on the evolution of 27w.
seas will slowly diminish Monday, however as tropical depression
27w is expected to turn and head back toward the marianas, the
seas should increase again. The exact amount of increase will
depend greatly on exactly how much it intensifies and exactly how
close it comes.
typhoon lan is headed in the general direction of Japan. It is
currently generating large swells that are affecting the marianas,
and could begin to affect micronesia. Tropical depression 27w is
currently a rather sheared system. Because of the shear, it is
currently moving southeast, a very unusual direction. It is
expected to escape to a region of lower shear, then start moving
in a more northwest direction. It will then bring increased seas
and winds to the marianas, exact amounts to be determined.
satellite and ascat analysis show tropical depression 27w as a small
exposed low-level circulation northwest of Chuuk at 9n148e. Rainfall
could be heavy at times for Chuuk state tonight and Monday. Also, a
surface trough is stretched along 10n across northern Chuuk, Pohnpei
and Kosrae states to the northeast rmi. Extensive clouds with patchy
showers and a few thunderstorms are over much of this forecast area
between the Equator and 10n-12n. Models indicate the pattern will
edge westward and weaken in the coming days. Drier weather should
arrive at Majuro on Monday and develop westward this week.
Sea conditions could be rough at times for Chuuk state. Long-period
west-northwest swell generated by distant typhoon lan will arrive at
Chuuk, Pohnpei and Kosrae during the next few days. This swell will
cause surf to build Mon thru Wed, and surf could approach hazardous
criteria, especially at Chuuk. Majuro/Kalo buoy currently shows
combined seas near 6 feet.
the monsoon trough remains across the Philippine Sea well north the
Palau and Yap, curving southeastward through dew point 27w currently just
northwest of Chuuk. Models show dew point 27w eventually moving northwest
along the trough, passing south of Guam Tuesday, then north of Yap
about Wednesday. But, lots of uncertainty in that forecast. At any
rate, a strong and moist monsoon flow is expected to develop
across Yap and Palau in the coming days and persist until later
Long-period swell from distant typhoon lan will produce hazardous
surf across Palau and Yap through mid-week. The swell direction will
gradually shift to the northwest overnight and Monday. Hazardous
surf on west facing reefs of Palau and Yap will spread to north
GU...high surf advisory from 6 PM Monday to 6 PM chst Wednesday for
High surf warning until 6 PM chst Monday for guz001>004.
Marianas waters...Small Craft Advisory from 5 am Monday to 6 PM chst
Wednesday for pmz152>154.
Hazardous seas warning until 5 am chst Monday for pmz152>154.
Small Craft Advisory until 6 PM chst Wednesday for pmz151.