Area Forecast Discussion
Issued by NWS Tiyan, Guam

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FXPQ50 PGUM 242010
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
610 AM ChST Sun Aug 25 2019

.Marianas Synopsis...
Partly cloudy skies and isolated showers are present across the
Marianas this morning with moderate southeast winds. Radar shows
scattered showers out west of the islands, with very few showers
seen to the east. Combined seas are running 4 to 5 feet at the buoys,
divided between east and west swell. Satellite shows the JTWC invest
area 99W centered near Yap, but extending its circulation across
the Marianas.

&&

.Discussion...
Have made only a few minor changes to the forecast, mainly extending
isolated thunderstorms through the day on Tuesday. Still expect
scattered showers to re-develop again later this morning in the
moist, unsettled conditions provided by 99W, but likely not as much
rain as on Saturday.

&&

.Marine...
The buoy at Ipan on Guam`s east side shows east swell at 4-5 ft,
while the Ritidian buoy shows 3-4 ft of west swell. Over the next
few days, WW3 guidance has diminishing swell from both directions,
until by Wednesday only a 3-4 ft east swell remains. The rip risk
should stay moderate along east facing reefs, but may drop to low
at times the last half of the week.

&&

.Tropical systems...
Invest 99W is shown on satellite as a sprawling but disorganized
circulation centered near Yap, with 15 kt winds occasionally hitting
20 kt, and the main areas of convection extending westward from the
center, and out east and southeast of the center, well south of
Guam. Little development is expected over the next day or two, but
Yap and Palau could see locally heavy rain today and tonight. Any
significant development should hold off until 99W is well out in
the Philippine Sea.

&&

.Eastern Micronesia and Chuuk...
The southeastern end of a monsoon trough is gradually weakening
across the region. A ridge has formed near Chuuk and Pohnpei and it
should maintain drier conditions for Chuuk thru Monday and Pohnpei
thru tonight. To the east, trade winds are filtering westward across
the Marshall Islands and Kosrae. A series of modest trade-wind
disturbances will trigger periods of showers and a few thunderstorms
near Kosrae by this afternoon and Majuro thru Monday. As trade
winds push farther westward, these disturbances will also affect
Pohnpei by Monday afternoon and Chuuk by Monday night. Latest ASCAT
and IR satellite reveal a trade convergent zone between 3N and 7N,
stretching east-northeastward from the Date Line to beyond 160W.
This feature is going to prolong unstable weather across the entire
region thru midweek.

&&

.Western Micronesia for Yap and Koror...
Invest 99W can be seen centered near Yap around 9N139E this morning.
Converging west to north winds just west of this circulation have
been coupling with a mid-level trough to produce widespread deep
convection across far Western Micronesia. This trend will continue
thru tonight. Rainfall amounts from nearly half an inch to an inch
and a half have been reported across Palau and western Yap State
for the past 12 hours. A similar amount of additional rainfall is
probable by Monday morning. Once this circulation has moved into
the Philippine Sea north of Koror and Yap Monday afternoon,
convergent monsoonal southwest winds are expected to sustain
periodic showers and thunderstorms for both locations thru Tuesday.
By midweek, surface ridging should develop over the area and promote
stable conditions.

Modest monsoonal swell and wind waves will maintain moderately
higher seas and surf across the Republic of Palau and Western Yap
State for the next few days. For now, both parameters should stay
below hazardous criteria but the risk of rip currents will increase.
If a stronger monsoonal band develops south of 99W Monday and
Tuesday, seas and surf will build higher and should be monitored
closely.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
Marianas Waters...None.

&&

$$

Middlebrooke/Chan


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