textproduct: WSO Pago Pago

DISCUSSION

The latest satellite imageries show deep convections associated with Invest 99P (99P) concentrated over the Swains Island area. Light surface winds for 99P together with low vertical wind shear (10 to 15 mph), and moderate upper-level outflow, makes for a favorable environment for 99P to further develop as it migrates east-northeast. Model solutions are also in agreement with moving Invest 99P east-northeast of the territory as it intensifies within the next 24 to 48 hours. Upper air observations (RAOB) from this afternoon (29/00Z) shows an unstable atmosphere with strong thunderstorm signature, and drier air mass over Tutuila, Aunu'u and the Manu'a Islands. Thus, expect numerous to widespread showers with potential thunderstorms and gentle to moderate southerlies for tonight through at least Tuesday. By early Monday morning, models are showing the center of 99P northeast of the Manu'a Islands, posing minimal to no threats to the territory. Winds will remain at moderate to fresh (15 to 20 mph) southerly breeze for the Manu'a Islands as gentle to moderate (10 to 15 mph) southerly winds prevail over the rest of American Samoa through the end of the short-term forecast period.

As model data projects Invest 99P to migrate further east then south of the area of responsibility (AOR) by midweek, the trough line will likely remain north of the territory before migrating south. Expect scattered showers with light and variable winds to remain for this period through at least the weekend. By midweek, model solutions show another low pressure system developing to the west-northwest of the Fiji Islands and migrating over Fiji as it intensifies. Models also show a trough to the east-northeast moving westward simultaneously as the aforementioned low pressure system. These two features will create a convergence area just west of the Samoa Islands by Saturday afternoon. Uncertainties in timing and locations of the features will likely be determined throughout the forecast period as more data becomes available.

There is a moderate chance for Invest 99P to intensify within the next 24 to 36 hours.

Marine

Combined seas have been observed to remain calm for the last couple of days. However, abrupt elevation of seas from thunderstorms embedded within the trough line has prompted an advisory for small crafts. Models are showing seas to remain between 5 to 7 feet for the rest of the forecast period. Additionally, with the center of Invest 99P located just north and east of the Manu'a Islands, seas are expected to elevate for the Manu'a coastal waters as moderate to fresh southerly winds move into the area, tonight. As soon as Invest 99P migrates east- northeast of the area, seas will also begin to subside for the Manu'a Islands. Otherwise, seas will likely remain favorable for the rest of the territory for this forecast period.

PPG WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory remains in effect for Swains and the Manu'a Islands. Flood Watch remains in effect for Swains Island