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FXPQ60 PGUM 212013

Area Forecast Discussion
National Weather Service Tiyan GU
613 AM ChST Sun Jul 22 2018

.Marianas Synopsis...
Two developing disturbances, one west of the Marianas and the other
well northeast, are evident on satellite. Another area of showers and
thunderstorms is seen along the monsoon trough to the east of the
islands. Partly cloudy skies with isolated showers and gentle to
moderate winds prevail over the area. Latest buoy reports show seas
between 3 and 5 feet.


A monsoon trough extends northeastward from a developing disturbance
centered near 12N139E across the Marianas to another developing
disturbance centered near 21N159E. An area of divergence associated
with the Tropical Upper Tropospheric Trough (TUTT) is enhancing an
area of convection to the east of the islands along the monsoon
trough. As the TUTT and monsoon trough continue to drift
northwestward, this band of convection is expected to move over the
CNMI this afternoon and then also over Guam tonight. The monsoon
trough will remain over the area for the next couple of days, keeping
showery and breezy conditions over the islands through at least
Tuesday afternoon. Heavy rain is possible at times Monday into
Tuesday. As the trough slowly drifts more towards the north, shower
coverage will decrease, however, an unstable pattern will continue
through most of the week. By the end of the week, surface ridging
will move into the area, bringing a drier pattern back to the
Marianas for the weekend.


Gentle to moderate monsoonal winds this morning are expected to
become moderate to fresh later this morning and continue for the next
few days. Winds could reach Small Craft Advisory criteria late
tonight or Monday. Along with the winds, seas are also expected to
slowly build over the next few days. Seas are not expected to reach
Small Craft Advisory levels at this time, however, the west swell
component could build enough to result in hazardous surf conditions
and a high risk of rip currents along west facing reefs on Monday.
this will be monitored closely to determine if any advisories are


.Tropical systems...
Two developing disturbances are evident on the latest satellite data
and ASCAT. Invest 96W is centered near 12N139E and Invest 97W is
centered near 21N159E. Both of these systems are subjects of a
Tropical Cyclone Formation Alert (TCFA) by the Joint Typhoon Warning

96W currently shows increasing convection near the center as it
drifts west-northwestward. latest model guidance shows this system
developing over the next few days as it moves northwestward over the
next few days. This system is currently not a threat to the Marianas.
For more information on 96W, see bulletins issued by the Joint
Typhoon Warning Center under WMO header WTPN22 PGTW.

Latest model guidance also shows 97W developing slowly as it
continues to drift north over the next few days. This system is also
not currently a threat to the Marianas. For more information on 97W,
see bulletins issued by the Joint Typhoon Warning Center under WMO
header WTPN21 PGTW.

A third area of unsettled weather is located east of the Marianas
along the monsoon trough that connects these two systems. Upper-level
divergence associated with the TUTT is enhancing convection in this
area. These showers and thunderstorms will slowly approach the
islands through the day, affecting the CNMI this afternoon and all of
the Marianas tonight into Tuesday.


.Eastern Micronesia...
A surface trough extends east-northeast across the region from near
Pohnpei to beyond the date line at 9N. Showers and thunderstorms
persist across much of the region this morning but with a lull in
showers at Majuro. Models still show a drier pattern emerging by
Monday with light trades across much of the region. Increased low-
level convergence and weak surface troughing will bring in another
period of unsettled weather to the region by midweek.


.Western Micronesia...
A weak ridge over Chuuk will keep fair weather conditions in place
the next several days. Expect only isolated showers and gentle winds
into the new week. A weak disturbance near Pohnpei could bring a few
more showers and a chance of thunderstorms Tuesday and Wednesday.

The tropical disturbance west of Guam will keep to the north of Yap
as it continues NW. This disturbance will continue a steady
strengthening trend which will also strengthen the monsoon flow over
Yap and Koror. Ridging will slowly wedge in from the east as the
disturbance lifts northward. This will bring drier weather in to
both locations on Monday. IR satellite currently shows Yap and Koror
on the southern edge of deep convection, but more weather southwest
of Koror. Winds and seas will stay elevated at Yap the next few
days, but seas and surf should keep below hazardous levels.


Marianas Waters...None.


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