Drought in Guam, May 1 to 31, 2021

Area Forecast Discussion
National Weather Service Tiyan GU
652 PM ChST Fri Apr 30 2021

.Marianas Synopsis...
Partly cloudy skies with spotty light showers and gentle to moderate
trade winds prevail across the Marianas this evening. Buoys show
seas between 6 and 8 feet.

&&

.Discussion...
little change made to the forecast. A dry trade-wind pattern is now
in place across the Marianas with little rainfall expected through
the next week. Latest model runs show little rainfall through next
Wednesday, with the GFS showing around one half inch across the
islands and the ECMWF a bit lower, with totals of around one quarter
inch. By Thursday, latest guidance indicates increasing showers and
thunderstorms over the region as an upper-level trough and possibly a
weak low develops to the west of the islands. This trough/low
combined with weak trade-wind trough could bring showers and
thunderstorms to the region for the end of the week. Since
confidence in this remains low, added a chance of showers and
thunderstorms for the end of next week.

&&

.Marine...
Latest model guidance continues to perform very poorly. Both the
GlobalWave and GFSWave models indicate seas of 4 feet over the buoys
at the current time while actual seas range from 6.5 feet at Tanapag
and 7.2 feet at Ritidian. It's obvious that the models are not
picking up the larger north swell that continues to dominate across
the region. Latest altimetry data shows seas of 8 to 10 feet to the
west through north of the waters. Based on altimetry, the high surf
advisory was extended through Saturday afternoon, when the north
swell should finally begin to subside, allowing surf to fall below
hazardous levels. The rip current risk will also remain high along
north facing reefs through Saturday afternoon. Seas of 6 to 8 feet
will continue through Saturday, then fall to between 5 and 7 feet by
Saturday afternoon. Seas will then subside further, to between 4 and
6 feet Sunday evening.

Gentle to moderate trade winds are expected to continue through the
weekend, then increase to occasionally fresh Monday.

&&

.Fire weather...
A dry trade-wind pattern will dominate over the island for the next
several days, resulting in little rainfall through the middle of next
week. The KBDI decreased slightly, to 626, as a few showers brought
needed rain to the island Thursday. As the drier pattern continues
over the next few days, the fire hazard, and KBDI, will likely
increase. As winds also increase early next week, a fire weather
watch or red flag warning may be needed.

&&

.Eastern Micronesia and Chuuk...
A trade-wind trough is interacting with upper-level divergence. This
set up, is favorable for widespread showers, and is causing showers
and thunderstorms across Kosrae and Pohnpei State. This is a similar
set up to last night, but divergence has weakened and heavy showers
are not expected.

In the near term (tonight and Saturday) showers will lessen around
Majuro as the convergence moves westward. As the showers move west,
they will be replaced by dry air from the trade winds. While heavy
showers are not expected tonight, showers will be widespread and
frequent thunderstorms could occur across Kosrae and Pohnpei State
tonight and reach Chuuk Saturday morning. Towards the end of the
weekend, the region will become more stable, as the trade winds
bring in more dry air. Around Wednesday, models are coming into
agreement that another round of showers will move through the area.
These showers will be from a series of trade-wind troughs, and
should reach the RMI around Wednesday.

Hazardous surf is still impacting Chuuk and Pohnpei, with surf
between 7 and 10 feet along north facing reefs. Models have done a
very poor job, and have underestimated this north swell event.
Hazardous conditions are expected to continue through Saturday
evening.

&&

.Western Micronesia...
A weak line of showers passed over Yap earlier today and the showers
are currently near Koror. Patchy showers will continue on and off
for the first half of tonight at Koror. Around Yap, partly cloudy
skies won't produce much rain, and conditions will remain calm. Once
this line passes Koror, the rest of the weekend conditions should
remain calm as there is no forcing in the lower levels. By the start
of the week, a circulation south of Chuuk will slowly lift northward.
This will cause an increase in showers and isolated thunderstorms,
primarily for Koror. A little farther north at Yap, models are now
trending towards a drier period with very little convection expected
trough next Wednesday.

A high surf advisory remains in effect for Koror and Yap. This is
due to a long period north swell from a low east of Japan. These
hazardous conditions will remain until Saturday evening, then will
drop below hazardous levels.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Surf Advisory until 6 PM ChST Saturday for GUZ001>004.

Marianas Waters...None.
&&

Marianas: Kleeschulte
Micronesia: Slaughter