Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 100800
Area Forecast Discussion
National Weather Service Tiyan GU
600 PM ChST Sat Dec 10 2016
Satellite and radar shows showers exiting the Tinian and Saipan
waters. Saipan airport observations show that nearly a half inch of
rain fell during the afternoon. Much drier weather is seen to the
east with only a few clouds. Farther southeast, a surface trough and
mid-level circulation is generating showers northwest of Chuuk.
Marianas buoys show seas between 5 and 6 feet.
Not much change to the forecast except to indicate much drier
conditions tonight with only a slight chance of showers. The
disturbance to the southeast is still expected to bring showers to
the Marianas Sunday night and Monday. Clouds will begin to break up
Tuesday, but GFS time-height cross-section shows high-level
clouds lingering into midweek. Only isolated showers are expected
the rest of the week with GFS hinting at a couple of weak
disturbances that could bring small increases in cloud cover.
Moderate winds and seas around 4 to 6 feet are expected through the
weekend. Seas will drop about a foot early in the week, but then will
increase 1 to 2 feet later in the week. Surf will only see minor
changes, but the risk of rip currents will stay moderate.
The trade-wind disturbance has shifted west of Chuuk this afternoon.
This will allow dry trade winds already over Pohnpei to spread
westward over Chuuk this evening. Meanwhile, a low-level circulation
and associated trough will maintain wet weather near Kosrae and
Majuro thru Sunday. As these systems continue to move westward, the
same wet regime will also arrive at Pohnpei on Sunday and Chuuk on
Monday. A modest trade-wind convergent zone between 5N and 9N,
meanders eastward from just east of Majuro at 173E across the Date
Line to beyond 165W. This feature will prolong showery conditions
across the entire region thru early next week. Toward midweek, dry
fresh northeasterly trades should displace this feature to the south
and promote fair weather near Chuuk, Pohnpei and Majuro. Kosrae might
still be close enough to this feature that lingering clouds and a few
showers are possible.
Trade-wind swell and wind waves are expected to increase starting
next Monday night and will peak near midweek. Even though it is not
expected to be a very robust event, it will be in conjunction with
astronomical high tides across the region. Need to keep an eye on
potential coastal inundation hazardous surf, especially near Kosrae.
Reasoning for the Chuuk forecast is included under the Eastern
Micronesia section above.
A broad but weak low-level circulation is anticipated to persist near
5N139E south of Koror and Yap over the next few days. At the upper
levels, a trough is also seen in the vicinity of both places near
10N138E. Divergence related to this upper trough is already enhancing
convection near Koror this afternoon and this trend will continue
thru Sunday evening. Despite the presence of the upper trough, a very
dry air mass above 700mb should keep fair weather near Yap thru
Sunday afternoon. Starting Sunday night, a southeasterly flow should
develop aloft which will advect moisture across the region. Coupling
with a trade-wind disturbance pulling westward from south of Guam,
the chance of showers and thunderstorms should increase near Yap. For
Koror, wetness will likely prolong thru Tuesday. As this trade
disturbance passes west of Koror near midweek, a large dome of high
pressure will enter the East China Sea. This feature might be strong
enough to nudge the persistent circulation farther south of both
locations and allow drier northeasterly winds to dominate the area.