FORECAST DISCUSSION

FRIDAY 17thAPRIL 2026 – P.M SHIFT

TONIGHT & TOMORROW:

An instability area associated with a trough of a low-pressure system with sufficient moisture near the surface triggered afternoon convection over both major islands. These convection induced brief moderate falls in the southern and interior areas as recorded by surface operational data. In addition to that, the presence of an upper-level divergence coupled with surface heating was the main contributing factor for the enhancement of rainfall activities. Sounding trace 00Z from the Pago station indicated indices of unstable atmospheric conditions through the levels. Convections started to diminish during the sunset periods. However, the cloud band to the west of Savai’i continue to move over the island, being pushed by the westerly flow aloft. This situation is likely to maintain cloudy conditions with some showery and thunderstorm activity tonight for Samoa. Therefore, expect cloudy periods with some isolated showers, brief moderate falls and thunderstorms possible

SUNDAY THROUGH FRIDAY:

A high-pressure system currently centred east of Australia is expected to move eastward, pushing the South Pacific Convergence Zone (SPCZ) near south of Samoa during the weekend, and is likely to bring some showery conditions over the group. The easterly trade wind regime is expected to predominate in the new week. At mid-levels, a high-pressure ridge may linger over the region during this outlook period, providing light steering flow, which suggests a lack of vertical disruption to convective development. In addition, southwesterly to westerly winds aloft are forecast to dominate the uppers through at least Sunday, before an upper high moves over the region. Model also hinted a weak convergence ride ahead of the aforementioned high pressure system, possibly bringing some rainfall activities by Monday into Tuesday before the easterly winds take control of our weather situation.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King Poloa wave buoys as well as altimeter data indicate that wave heights have fluctuated below 2 metres over the past 24 hours. These wave activities are forecast to persist throughout this outlook period, posing no significant wave-related hazards to the islands’ marine waters.

ADVISORIES/WARNINGS:

NONE

Weather Duty Team:

LMSA & P. HUCH