Drought in Guam, October 1 to 31, 2020

Area Forecast Discussion
National Weather Service Tiyan GU
606 PM ChST Wed Sep 30 2020

.Marianas Synopsis...
West to southwest winds, showers and thunderstorms prevail over
the Marianas this afternoon.

.Discussion...
Little change made to the forecast. The active monsoon pattern is
continuing over the Marianas. Radar and satellite from this afternoon
depicted showers increasing from east to west as low-level
convergence and moisture rise. Still anticipate the possibility
of locally heavy showers tonight through Thursday night as models
continue to indicate that this is the time period of the highest
convergence. Models hint at a lull in activity Thursday, but kept the
numerous showers during that period as uncertainty in the change is
high. Showers will decrease but expect scattered showers and isolated
thunderstorms Friday through Saturday. Earlier forecast only had the
scattered showers through Friday night but enough moisture will be
present to keep the same coverage through Saturday.

Models show decreasing deep-layer moisture and this will allow shower
coverage to tapper off by Saturday night...although showers and
thunderstorms will still occur through Sunday. Only isolated showers
are expected Sunday night through Monday night as a weak ridge will
build across the local area. A surface trough passing over the
Marianas will cause a return to isolated showers and thunderstorms
Tuesday and Wednesday.

&&
.Marine...
Ritidian, Tanapag and Ipan buoys indicated seas between 2 to 4 feet
and all depicted an east to northeast trade-wind swell. This swell
should create surf of 2 to 4 feet along east facing reefs. Ritidian
and Tanapag buoys also had a north swell, and a west swell. Either
swell is not too large and expect only a low rip current risk the
next few days.

&&

.Eastern Micronesia and Chuuk...
A well defined trough stretches across Micronesia from Majuro to
Chuuk. This trough will continue to produce showers and isolated
thunderstorms for the rest of tonight.

Strong divergent flow aloft continued today boosting convection and
allowing for numerous showers across the region. This active pattern
will continue as more showers will be forming tonight because of the
trough. However, the convection will be weakening as we get closer
to the morning. As the trough lifts north ridging will move in
behind it allowing for a break in the weather. The time-height
across the region, along with downstream NUCAPS soundings, place a
block of dry air around 800 mb to 600 mb. While this will not be
enough to stop shallow convection it will be enough to stop
thunderstorms between Thursday to the first half of Friday.

By the weekend and into Monday another disturbance will begin to
form and more showers will are expected near Kosrae and Pohnpei. For
now models keep this disturbance to the north and east of Majuro but
the location of the system could change as it begins to form.
Combined seas will build slightly reaching 3 to 6 feet through the
weekend and into early next week.

&&

.Western Micronesia for Yap and Koror...
A monsoon trough continues to create showers and thunderstorms for
Koror and Yap. Convection in the region has weakened, but there is
still plenty of moisture and instability in the atmosphere. The
soundings for both Yap and Koror have Pwat values over 2 inches.
These moisture levels will not be decreasing over the next several
days. As the monsoon trough stays rooted in west Micronesia. This
means more opportunities for showers and thunderstorms through the
weekend and into next week. Combined seas will continue to stay
below hazardous levels.

&&

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

Ziobro/Slaughter