FXPQ60 PGUM 242100
Area Forecast Discussion
National Weather Service Tiyan GU
700 AM ChST Wed Apr 25 2018
Moderate trade winds and combined seas of 5 to near 8 feet are seen
across the Marianas this morning. A weak trough is dragging scattered
showers and isolated thunderstorms through the islands, already
affecting Tinian and Saipan, and approaching Rota and Guam.
Models continue to show unsettled weather for the Marianas the next
few days. A weak trough has already passed through the islands, but
is still setting off scattered showers and isolated thunderstorms
behind it across the Marianas. These should taper off around mid-
morning, with isolated showers and thunderstorms the rest of the
day. GFS and ECMWF still show a trade-wind surge coming in late
Thursday and Friday, setting off more scattered showers and isolated
thunderstorms Thursday afternoon through Friday night, with locally
heavy rain a possibility on Friday. The weekend still looks fairly
quiet as the mid-levels dry out.
Seas have increased in the last couple of hours to 7.5 feet at the
Tanapag buoy off northern Saipan, and as the morning progresses, seas
should settle in at 6 to 8 feet or so, with a 3 ft north-northeast
swell and up to 6 feet of east swell. This will keep the rip risk
moderate today and tonight with 5-7 ft surf along east facing reefs.
But then east swell will build a little on Thursday, possibly
resulting in a high risk, with the best chance for Tinian and Saipan.
This will be watched closely the next couple of days.
Showers and thunderstorms associated with a trough between Pohnpei
and Kosrae yesterday have steadily dissipated overnight leaving just
a few showers and mid/upper-level clouds in the area. Scatterometer
data indicate a series of trade-wind troughs throughout the region.
These troughs will bring periods of isolated showers and mostly
cloudy skies to the area in the short term, but a pattern change will
bring a more unstable weather pattern later in the week. The GFS,
ECMWF, and NAVGEM all show a near-equatorial trough stretching across
the area from western Micronesia between 5N and 7N, bringing
scattered showers and isolated thunderstorms to much of the region.
Over the weekend, some locations could see winds shifting to south
or even southwest. Seas will generally stay between 4 and 7 feet
across the area this week.
A weak circulation remains well SW of Chuuk near 4N146E, but all the
convection is displaced to the northeast. Models show little to no
movement the next several days. Instead, the trough moving west of
the Marianas will eventually link with the circulation, reforming
a near-equatorial trough across Yap before the trough shifts
southwest toward Koror. Not much change to the forecast, though, as
a dry short term gives way to increasing clouds and a few more
showers over the weekend. A few thunderstorms are possible Sunday at
Yap. Benign weather at Chuuk will become unstable with increasing
showers and thunderstorms by Friday as a trough develops across
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