Area Forecast Discussion
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FXPQ60 PGUM 200224

Area Forecast Discussion
National Weather Service Tiyan GU
1224 PM ChST Fri Jul 20 2018

Drier air associated with an upper-level trough has caused shower
coverage near Guam and Rota to decrease by late this morning.
Therefore, updated forecast to reflect this change.


.Prev discussion... /issued 628 AM CHST Fri Jul 20 2018/

Marianas Synopsis...
Mostly cloudy skies with scattered showers are seen across Guam and
Rota, while partly cloudy skies and isolated showers are occurring
over Tinian and Saipan. Gentle winds prevail across the Marianas. A
weak circulation is seen to the southeast of Guam. Latest buoy
observations show seas between 3 and 5 feet.

A weak circulation to the southeast of Guam has brought scattered
showers to Guam and Rota this morning. As the disturbance slowly
drifts toward the northwest over the next few days, slow development
is expected. this circulation will maintain increased showers over
Guam and Rota thru tonight, with isolated showers expected to return
by Saturday morning. At this time, the majority of the showers and
the risk of thunderstorms is expected to remain south of Tinian and
Saipan. Current model guidance shows little development with this
disturbance until it is well northwest of the Marianas.

As the circulation tracks further northwest, it will drag the
monsoon trough farther north over the Marianas. This will bring
another round of scattered showers to the Marianas Sunday and
continue thru Monday night. Latest GFS run shows quite a bit of rain
over the islands for the beginning of next week. If this holds true,
shower coverage may need to be increased for Monday and Monday night.
A much drier pattern is then likely to return to the region around
the middle of next week.

A west swell is now the dominant swell over the region and is
expected to slowly build over the next couple of days. This will
result in a moderate risk of rip currents along west facing reefs.
Enough east swell also remains to keep a moderate risk of rip
currents on east facing reefs as well.

Tropical systems...
Tropical Storm Ampil (12W) is seen on satellite well northwest of the
Marianas. Ampil is no threat to the Marianas at this time and is
currently moving toward Okinawa. For more information on TS
Ampil, refer to bulletins issued by the Joint Typhoon Warning Center
under WMO header WTPN32 PGTW and by the National Weather Service
under WMO header WTPQ32 PGUM.

Another weak tropical disturbance, Invest area 96W, is centered
southeast of Guam near 11N149E and is slowly drifting northwestward.
This system is expected maintain intensity as it moves through the
Marianas. Weak development is possible once this system is northwest
of the islands.

Eastern Micronesia...
A fairly quiet weather pattern persists across the region this
morning with showers and thunderstorms primarily south of Pohnpei
and near Kosrae. Weak trade-wind convergence will keep showers near
Kosrae the next couple days with scattered showers developing
tonight there and lingering into the weekend. GFS shows a weak
disturbance/circulation developing within the region on Sunday near
Kosrae that will be the focus of additional showers and
thunderstorms Sunday near Majuro and Pohnpei. Light/variable winds
and drier weather is expected for early next week.

Western Micronesia...
Quiet weather is seen at Koror and Chuuk this morning while isolated
showers and thunderstorms are near Yap. A monsoonal pattern will
prevail across the region the next few days as a weak circulation
southeast of Guam will be the main driving force of weather. The
monsoon trough and weak circulation will keep north of Yap and Koror
as the circulation heads slowly WNW or NW. Expect showery weather
and moderate to fresh southwest winds at Yap and Koror Saturday and
Sunday as the monsoon strengthens. Drier weather returns to Chuuk
this weekend and to Yap and Koror by Tuesday as a ridge builds south
of the monsoon trough.


Marianas Waters...None.


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