textproduct: WSO Pago Pago
This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.
Synopsis
Satellite imagery continues to reveal two key features of interest over the tropical Southwest Pacific: An equatorial trough just north of American Samoa (trough A); and a surface trough to the south and southeast extending from near Niue to French Polynesia (trough B). An important trend with trough B compared to yesterday's forecasts is that it has become less organized with westward extent. Satellite wind estimates and imagery indicate that the strongest convergence and associated heavy rainfall / thunderstorm activity is now positioned over French Polynesia, with convection near Niue and the Cook Islands weakening.
Long term [Wednesday through Sunday]
The convergence associated with trough B is forecast to remain south of the territory through the week. Therefore, winds are forecast to remain light at near or under 10 mph. However, there is a very small chance (~10%) that the convergence moves further north than currently projected, hence bringing breezy southeasterlies to the territory.
The trough is projected to remain in a relatively similar position throughout the week, allowing moisture to continue to deepen along the convergence and strengthen the trough. Model data projects a high likelihood of weak embedded low pressure areas developing within the convergence by late week into the weekend. In this scenario, winds are forecast to turn out of the northwest as flash flooding potential significantly increases over the weekend.
Marine
Despite the forecast decrease in wind speeds for American Samoa and coastal waters, the fresh breeze to the south of the convergence associated with trough B is expected to bring large southeasterly swells to the territory. Marine conditions are forecast to reach Small Craft Advisory levels tomorrow. Wave heights are forecast to peak Monday night into Tuesday in the 7 to 9 foot range with period times nearing 15 seconds. This will bring challenging navigation conditions for mariners and large surfs with strong currents to shorelines, especially along south and east facing shorelines. Small Craft and High Surf Advisories are likely for this timeframe.
PPG WATCHES/WARNINGS/ADVISORIES
NONE
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