Area Forecast Discussion
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FXPQ60 PGUM 252023

Area Forecast Discussion
National Weather Service Tiyan GU
623 AM ChST Wed Sep 26 2018

.Marianas Synopsis...
Partly cloudy skies with light and variable winds and isolated
showers prevail across the Marianas. Scattered showers are seen just
south of the Guam coastal waters. Buoys show seas between 2 and 5


Partly cloudy skies are seen across the region this morning with
scattered showers and a few thunderstorms seen to the south of guam
waters. A band of weak convergence to the southwest of Guam waters
will maintain the possibility of scattered scattered showers across
the southern Guam waters through the day along with isolated
thunderstorms. For Guam, light and variable winds will result in
island convection a little later this morning. Therefore, decided to
add scattered showers beginning around mid-morning for Guam for
today, with partly cloudy skies and isolated showers returning by
tonight. The big story for the remainder of the week is the weak
circulation centered to the southeast of Pohnpei. Model consensus
still brings this system through the Marianas over the weekend, with
an overall wet pattern likely. The models diverge, however, when it
comes to intensity of the system. The GFS remains the most aggressive
model, bringing the circulation across Guam as a significant
tropical cyclone Saturday morning. The ECMWF and NAVGEM also bring
the system over or near Guam, but as a much weaker system, with the
ECMWF being the weakest. It is too early to tell how strong this
circulation will get, but what is likely is that it will be a wet
weekend. Numerous showers and isolated thunderstorms are forecast to
begin friday night and continue through Sunday before decreasing to
isolated showers. By Tuesday, a fairly dry pattern is expected to
return to the Marianas.


Latest buoy data shows seas between 2 and 5 feet. Seas are expected
to be between 4 and 6 feet through today and begin to build later
this evening. Increasing west to northwest swell from distant Super
Typhoon Trami is expected to begin to arrive over the next few days.
Seas are expected to gradually build through the end of the week,
reaching 6 to 8 feet by Friday and possibly up to 10 feet over the
weekend. A High Surf Advisory is likely for Thursday and the
following few days. The disturbance approaching the Marianas from
south of Pohnpei could bring an additional increase in seas and surf,
depending on how it develops as it approaches.


.Tropical systems...
Invest 94W remains well southeast of Guam, just southeast of Pohnpei
this morning. This system continues to be monitored for any further
development by the Joint Typhoon Warning Center. The disturbance is
expected to approach the Marianas over the weekend, though model data
is very diverse on the intensity of this system as it moves across
the region. Stay abreast of any updates and possible bulletins
concerning the development of this system.


.Eastern Micronesia and Chuuk...
Widespread heavy showers and thunderstorms persist south of Chuuk and
Pohnpei along the southern edge of a surface trough and the
circulation, 94W. None of the scatterometer satellites got a good
pass overnight, so the current position, based on IR satellite is
still low-confidence, but it seems to be near 4N160E, which indicates
a slight eastward drift, which the GFS and, to a lesser extent, the
ECMWF, depict. The motion is expected with the surge of strong
westerly winds south of 94W. Overall the system remains disorganized
with little convection to the north. Current regional forecasts
closely follow the GFS with an eventual WNW track beginning Thu as it
slowly develops. Thus, increasing showers and thunderstorms are
expected at Pohnpei and Chuuk by Thursday, increasing that night at
Chuuk. Showers will increase at Kosrae tonight as convergence
increases within the southeasterly wind flow. Majuro stays fairly
quiet the next several days. Ultimately, the forecast is dependent on
the circulation beginning its WNW motion Thu. There have been some
circulations in past years that have lingered for days up to a week
before taking on that motion. Will ultimately have to keep an eye on
where the center is and how the convection develops around it.

Have issued a high surf advy for Kosrae as swell and wind waves are
expected to increase tonight from the S-SW. Seas and winds will
increase across the region with surf likely to become hazardous at
Chuuk and Pohnpei later in the week. Seas and winds may also become
hazardous for small craft late week as well.


.Western Micronesia...
Southwest monsoon flow continues to spark a few thunderstorms near
Yap, but Koror has dried out. Little change is expected the next
several days, but the developing circulation, 94W, passing somewhere
to the NE of Yap over the weekend will bring increasing clouds
beginning Saturday at Yap and possibly later in the weekend or early
next week at Koror.

Have issued a high surf advy for Koror and Yap with the expectation
that the long-period NW swell will continue to rise due to STY
Trami`s very slow motion. Surf is expected to become hazardous
overnight. This hazardous surf event will likely persist into early
next week.


Marianas Waters...None.


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