Area Forecast Discussion
Issued by NWS Tiyan, Guam

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000
FXPQ50 PGUM 270832
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
632 PM ChST Mon Jan 27 2020

.Marianas Synopsis...
Isolated showers and east winds prevail across the Marianas this
afternoon.

&&

.Discussion...
Some changes made to the forecast. Partly cloudy skies and isolated
showers will prevail over the Marianas through Wednesday night. Radar
and satellite imagery do show some clouds and showers just to the
east and south of the Marianas. While a brief period of clouds and
showers are possible models keep skies partly cloudy and showers
isolated through Wednesday night. A circulation was located south of
Chuuk this afternoon. Models keep this circulation weak but move it
to the northeast. It is predicted to be located just south of Guam by
Saturday. Models also show that it will interact with a shear line
that will move south and over the Marianas this weekend. Moisture
will increase ahead of these weather features and cause mostly cloudy
skies Thursday through Friday. The circulation and shear line is
expected to produce scattered showers and isolated thunderstorms
Saturday through Sunday night. Winds will mainly be between 10 to
15 mph through the week increasing to 10 to 20 mph with a few gust
the coming weekend.

&&

.Marine...Observations from Ipan and Tanapag buoys show seas between
6 to 8 feet A swell from the east was observed by both buoys. Models
indicate a north swell passing over the area. Both buoys may be
blocked and not able to observe this north swell. Both swells will
persist through the forecast. The north swell will remain near 2 feet
through the forecast. The east swell is between 5 to 7 feet and is
generating a high rip current risk on east facing reefs. The east
swell will remain this high through Wednesday decreasing by the late
afternoon on Wednesday. Seas and winds did decrease enough to allow
the small craft to be canceled. Winds and seas are expected to
increase by the weekend.

&&

.Eastern Micronesia and Chuuk...
A disorganized circulation/disturbance is centered southwest of
Pohnpei near 5N155E. Convergent trade flow is triggering patchy
showers/thunderstorms southeast of Majuro to beyond the dateline.
Fresh to strong trade winds are now confined to the Marshalls, near
Pohnpei, and waters between 10N and 15N.

As highlighted in the previous discussion...models have struggled to
resolve disturbances embedded in the near-equatorial trough across
eastern Micronesia recently. This leads to greater uncertainty
overall, even for the short-term. Main adjustment to the forecast
was delaying scattered showers for Chuuk until Tuesday evening since
circulations have been transient and any convective masses have been
reluctant to drift west of Pohnpei up to this point. Still expect a
circulation to develop and maintain some integrity as it drifts west-
northwest as the week progresses. Trade convergence east of the
circulation may prolong showery weather for Chuuk through Thursday
and possibly Friday if the pattern stalls further. Trade-wind
convergence associated with the ITCZ should drift northward across
Majuro by late Wednesday into Thursday...introducing a showery trade-
wind pattern that may persist into Friday. Expect these showery
trades to spread to Kosrae during the weekend locations farther east
early next week.

Persistent trade-wind swell, wind waves and residual long-period
north swell will maintain hazardous surf on Majuro thru tonight,
Pohnpei and Chuuk thru Tuesday, and Kosrae thru midweek. Hazardous
marine conditions for small craft will continue near all four
locations through at least Tuesday night. A new long-period north
swell will arrive Wednesday night. This may cause surf to become
hazardous again on Pohnpei and Kosrae.

&&

.Western Micronesia for Yap and Palau...
Gentle trade winds and partly cloudy skies are expected across far
Western Micronesia thru at least midweek. A shearline is
southeast of Guam. Guidance indicates this shear line should lift
north to the east of Yap. In the event it continues
eastward...expect a boost in showers and trade winds by Thursday.
For Palau, light winds may encourage more clouds and showers the
next few days, with dry air being the primary inhibitor for deep
convection/heavier showers. It still looks like there is a decent
chance for a wetter regime this weekend as a weak
circulation/tropical disturbance edges in from the east while a
frontal boundary/shear line drops down from the north. The
evolution and timing of these two features is crucial...with
confidence is too low to increase shower coverage at this time.
Seas of 4 to 7 feet are expected through the week.

$$


.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through Wednesday afternoon for GUZ001>004.

Marianas Waters...None.
&&

$$

Ziobro/Bukunt


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