000
FXPQ50 PGUM 152236
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
836 AM ChST Fri Apr 16 2021

.Marianas Synopsis...
Partly cloudy skies and gentle to moderate trade winds prevail.
Satellite shows very little in the way of shower activity over and
immediately upstream to the east. Typhoon Surigae (02W) is centered
roughly 750 miles to the southwest of Guam near 8.7N 134.8E.

&&

.Discussion...
Looks like a fairly dry day is in store with a dry air mass and
featureless trade winds. Could be a great sunset today with the tufts
of cirrus clouds wafting overhead from Surigae far to the southwest.
A slight uptick in shallow trade-wind showers tonight and early
Saturday as gentle trade flow impinges on the outer periphery of
Surigae`s wind field. Overall though it looks dry for through the
weekend with a thick layer of dry air capping the boundary layer. The
break down of winds around the middle of next week could lead to
some shallow island-effect showers during the daytime.

Both the GFS and ECMWF hint at a period of south to southwest winds
for the Marianas late next week as  as the system is absorbed into
the mid latitudes. What does this mean for the Marianas? It could
introduce a wetter pattern late next week. Given how far out it is,
kept a dry season outlook of partly cloudy skies and isolated
showers.

&&

.Marine/Surf...
Combined seas of 5 to 7 feet are expected the next several days.
Seas will be composed mainly of northeast swell and wind waves from
the east the next day or so. By Saturday, southwest swell will start
to filter in from Surigae. This will be the beginning of a prolonged
period of southwest swell that gradually shifts to the west then
northwest. Some very large west swell events for the Marianas
involve an expansive area of fresh to strong monsoon winds with a
typhoon anchored to front end of the monsoon flow. This setup with
Surigae has some elements of this recipe. Hazardous surf seems likely
next week with the details being ironed out as variables become
clearer.

&&

.Fire weather...
The KBDI is in the extreme category at 706 due to the recent stretch
of dry weather. Fortunately, winds are expected to stay gentle to
moderate so don`t expect grass fires to run amok.

&&

.Climate...
An impressive westerly wind burst (WWB) has taken place along the
equator south of Palau/Yap the last 10 days or so. This WWB owes its
existence to a strong Madden Julian Oscillation propagating through
the region from west to east. This intraseasonal event will act to
push the climate system back to ENSO neutral conditions. An ENSO
outlook for the fall is tricky at this time as the spring
predictability barrier is in full swing. This can often create
conflicting signals as to the expected state of ENSO late in the
year. On one hand, this event has all the hallmarks of a push towards
the warm side of ENSO neutral. On the other hand, first year
moderate La Ninas (like 2020) have historically been followed by La
Nina the following year. There is support for both sides at this
time.

&&

.Tropical systems...
Now Typhoon Surigae (02W) is centered just north of Kayangel in the
Republic of Palau near 8.7N 134.8E and continues to move very slowly
towards the west overall. Surigae wobbled WSW overnight. This wobble
to the WSW may be linked to the vast majority of deep convection
anchored to the south side, acting to pull the center towards this
persistent convective area to the south. Surigae`s meandering motion
and intensification just north of Palau has led to high end tropical
storm conditions across Koror, and likely typhoon conditions for
Kayangel at 8N latitude. Strands of heavy monsoon showers have also
blossomed across the southern islands of the Republic of Palau.

Kayangel and Koror/Babeldaob area will continue to get pummeled by
strong winds and bouts of torrential rain today. An automated
weather station on the barrier reef west of Koror measured over 17
inches of rain since yesterday morning. Conditions should begin to
improve late today. See the western Micronesia discussion for
detailed information.

&&

.Eastern Micronesia...
Surface analysis from early this morning showed a surface trough
just east of Kosrae. Trade-wind convergence east of the trough was
producing an area of scattered showers and isolated thunderstorms
over the Marshall Islands. An upper-level trough over the area was
also helping to produce the activity mentioned. Scattered showers and
isolated thunderstorms are expected over Majuro today and tonight. As
the area moves westward shower activity will taper off at Majuro
becoming isolated by Saturday. The westward movement of the activity
will bring scattered showers and isolated thunderstorms to Kosrae
this afternoon. The scattered showers and isolated thunderstorms will
persist at Kosrae through Saturday night. Scattered showers and
isolated thunderstorms are also expected at Pohnpei starting tonight
continuing through Tuesday. Models show a circulation developing near
Wake Island by Sunday. This will cause southeast winds over the area
by the end of the weekend.

&&

.Western Micronesia...
The main concern for the western half of Micronesia is Typhoon
Surigae. The typhoon is moving slowly west-southwestward this morning
while also intensifying. As Surigae intensifies the wind field will
expand slightly. The slow movement and expanded wind field suggest
that Koror will remain in tropical storm conditions through the day.
The typhoon is predicted to be far enough away from Koror that winds
should begin to decrease by this evening. Rainfall has been quite
heavy over Palau and eTrap estimate predict another 5 to 10 inches
possible through the day. Showers will likely be heavy at times
through tonight. Convergence south of the typhoon will produce
scattered showers and isolated thunderstorms across Palau Saturday
and Saturday night. With the ground saturated from previous rainfall
flooding is likely through tonight with mudslides another
possibility. With the typhoon so close to Palau seas and surf will be
dangerous through the day. Coastal inundation is also possible
across Palau along north and west facing reefs. Yap is far enough
away from Surigae that tropical storm conditions are not expected
there. Yap is close enough to that scattered to numerous showers and
isolated thunderstorms are expected there through Saturday night.
Elevated winds and seas will also be hazardous to small craft through
at least tonight. Chuuk is far to the east of the activity and only
isolated showers are expected there through Monday. Models show a
circulation forming near Chuuk next week and is expected to generate
scattered and isolated thunderstorms there on that day.

&&

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

$$

Marianas: Bukunt
Micronesia: Ziobro