National Weather Service United States Department of Commerce

FXZS60 NSTU 280056

Area Forecast Discussion
National Weather Service Pago Pago AS
156 PM SST Fri Mar 27 2020

.Forecast Discussion...

A shear line, extending for a low pressure system well to the
southeast of the territory, remained over the Tutuila and Aunu`u
throughout the morning and early afternoon hours. Heavy rain fell
at times which prompted a Flood Advisory in the region.

The shear line is expected to remain nearly stationary tonight and
into tomorrow morning. The recent balloon launch shows the
atmosphere is very moist and unstable. The shear line helps to
provide lift and produce showers in the region. Showers became
scattered this afternoon, however the shear line is forecast to
move back over American Samoa later tonight to produce similar
conditions like we had earlier today. Therefore, showers are
expected to become numerous later this evening and will last
through tomorrow morning.

As the low pressure system recedes further south, the shear line
will move away from American Samoa throughout the afternoon
tomorrow. A weak ridge of high pressure will move over the Samoan
Islands and theta-e values are shown on global models to greatly
decrease. Clouds coverage will decrease, however scattered showers
will be in the forecast for Saturday afternoon and evening as the
marine layer still remains moist and indices remain favorable for
atmospheric instability in the region.

Drier air is expected on Sunday with isolated showers. The weather
pattern will be slow moving next week, therefore similar
conditions are forecast for the majority of next week. Also, the
likelihood for tropical development remains very low for the next
7 days.



The latest information from the PacIOOS near Aunu`u shows sea
heights of around 6 feet throughout the morning and early
afternoon hours. Seas are forecast to remain around 6 to 7 feet
tonight and the weekend as periods are expected to about 11 to 13
seconds. There are no significant weather patterns that would
build seas to advisory criteria this weekend, however may reach
the lower criteria for a Small Craft Advisory by Tuesday. We will
closely monitor conditions for early next week.