textproduct: WSO Pago Pago

Long term [Tuesday through Saturday]

The ridge of high pressure generating the southeasterly trades will shift eastward by mid through late week. This will lead to winds turning more easterly as the high moves to the southeast of the territory. ECMWF and GFS guidance indicate wind speeds decreasing by late Tuesday as this transition occurs.

Following the transition into an easterly flow regime, Considerable uncertainty is present regarding the wind speeds and rainfall pattern for the latter half of the week. The exact positioning of the high pressure system and associated pressure gradients will be critical over this period. Model and ensemble guidance generally indicates stronger trade winds east of the territory and weaker winds to the west, but with significant differences in exact positioning. GDPS, UKMET, operational GFS, and GFS ensemble all indicate wind speeds again increasing to near Advisory levels over the latter half of the week. Meanwhile, the ICON, operational ECMWF, and ECMWF ensemble keep winds much more modest in the 10 to 15 mph range, with the stronger winds displaced further east.

These differences in the wind pattern will also have a significant impact on rainfall potential. Easterly winds decreasing in speed from east to west creates "speed convergence." Convergence forces air upward which creates more favorable conditions for increased rainfall. UKMET, operational GFS, and GFS ensemble are the most bullish for rainfall potential, depicting the speed convergence creating a surface trough axis near the territory. Meanwhile, other guidance keeps the most significant rainfall activity north and west of the islands. Regardless, increasing atmospheric moisture associated with the transition to easterly winds should at the very least bring more favorable conditions for passing showers.

Therefore, expect winds to shift from southeasterly to easterly by midweek, with at least a slight increase in rainfall likely. However, significant uncertainty remains regarding the strength of the easterly winds and the magnitude of the increased rainfall.

Marine

Observations from the PacIOOS Aunu'u buoy have indicated wave heights ranging from 8 to just over 10 feet since Wednesday night as trade winds developed across the area. Large seas, Advisory level surf, and increased rip current potential should persist and potentially slightly increase through early Tuesday as trade winds remain at a fresh breeze.

Marine and surf conditions are expected to at least briefly improve on Tuesday night as wind speeds temporarily decrease into a gentle to moderate breeze during the aforementioned transition to easterly flow. However, seas will still be choppy at around 7 to 9 feet. Wave and surf heights beyond Tuesday night will be heavily dependent on the aforementioned uncertainty in wind speeds, but are likely to increase at least slightly.

PPG WATCHES/WARNINGS/ADVISORIES

High Surf Advisory Small Craft Advisory