FORECAST DISCUSSION
FRIDAY 17thAPRIL 2026 – A.M SHIFT
TODAY:
A surface weak trough of low-pressure lies over Samoa, inducing sufficient moisture and atmospheric instability, with light and variable winds. This weather system is triggering deep convection to the west of the group, which is enhanced by an upper diffluence overhead in that region. The morning sounding trace from Pago (16/12z) indicates a fairly moist low-level vertical profile with sufficient convective potential energy and precipitable water reaching 54.70mm. However, upper data reveal a weak vorticity environment at 850mb over the forecast area with a strong deep-layer wind shear. These environmental conditions may couple with a high-pressure system generally dominating the mid-level atmosphere, likely inhibiting widespread significant convective storm development. In addition, a weak northerly low steering flow (700-850mb) persists, with a moderate to strong southwesterly upper steering (200-700mb) directing convection near the west of Savai’i today. But for the rest of Samoa, afternoon thunderstorms are likely in the afternoon, particularly over the interior highlands, and may bring moderate falls.
SATURDAY THROUGH THUSRDAY:
Global weather models suggest that gentle to moderate easterly trade winds will dominate the surface through at least 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. These synoptic weather patterns may inhibit significant widespread convection over Samoa, although localised moderate to heavy falls are still likely in parts of the group.
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:
F. Kalapani, A. Sofeni, N. Tutasi & C. Baker.