Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 232108
Area Forecast Discussion
National Weather Service Tiyan GU
700 AM ChST Fri Mar 24 2017
.Marianas Synopsis... East winds, patchy cloudy skies and
isolated showers prevail across the local area this morning.
Little change made to the forecast. Updated winds with new GFS
model data. Surface analysis from Thursday night indicated a shear
line draped across the Marianas. Satellite imagery showed patchy
clouds over the Marianas this morning with the major concentration
over Tinian and Saipan. Models keep the shear line weak and it
will just generate patchy clouds through much of the day. Showers
will be isolated at best.
Dry season weather will prevail through the weekend as moisture
will remain shallow with partly cloudy and isolated showers
expected. Saturday is particularly dry with mostly sunny skies
Moisture is predicted to increase slightly over the Marianas on
Monday. There will be enough moisture to produce patchy clouds,
but not enough to produce nothing more than isolated showers.
Observations this morning from the Ritidian, Tanapag and Ipan
buoys indicate combined sea heights of around 4 feet. A north
swell and an east swell were present. The seas are about a foot
lower than model predictions. Buoy data shows the north and east
swell at 3 feet, which is also lower than model projections.
Lowered seas and swell height for today and tonight so as to agree
with current buoy data. The north and east swell should increase
by about a foot on Saturday which will increase slightly the
combined sea height and also the surf on the north, east, and west
facing reefs. Winds will remain between 10 to 15 knots through
A trade-wind disturbance is approaching Chuuk, while another one
is east of Kosrae this morning. This first one will spread showers
and possible thunderstorms to Chuuk by noon today. The second one
should also arrive at Kosrae this evening and then Pohnpei on
Saturday with similar conditions but will pass south of Chuuk.
After the passage of these disturbances, drier trades near Majuro
will shift westward and provide a period of fair weather for
Chuuk, Pohnpei and Kosrae this weekend. A surface trough has
crossed the Date Line this morning and will be closing into the
Marshall Islands this evening. It will interrupt the drier
conditions near Majuro tonight and Saturday, bring back showery
weather to Kosrae this weekend, Pohnpei and Chuuk early next week.
Another surface trough is also present farther east upstream near
165W. This system could bring back wetness to Majuro early next
week, and prolong instability for the rest of the locations thru
midweek next week.
A long-period north swell generated by strong to near-gale winds
southeast of Japan earlier will persist from Chuuk State eastward to
the Marshall Islands over the next several days. Meanwhile, trade-
wind swell and wind waves are anticipated to build by this weekend
across the region. This combination will cause seas and surf to
rise, and conditions need to be monitored for possible High Surf and
Small Craft Advisories. In conjunction with an astronomical high
tide cycle of 5 to 6 feet above Mean Low Low Water levels early next
week, coastal inundation is also possible at Kosrae and Majuro.
Chuuk forecast discussion is included with Eastern Micronesia
Latest sounding data from Koror and Yap reveal mid-level moisture
creeping northward over the islands from the south. At the lower
levels, a trade-wind disturbance is passing southeast of Yap this
morning. This feature might spark off a few thunderstorms near Koror
tonight and Saturday. By Saturday night, moist air will be present
thru out the whole vertical column above both places. With more
disturbances arriving from the east, a relatively wet week is in
stored for Koror and Yap next week.