FORECAST DISCUSSION
THURSDAY 14thMAY 2026 PMSHIFT
TONIGHT:
Fair weather conditions continue to persist across Samoa as easterly trade winds remain prevalent. Meanwhile, the South Pacific Convergence Zone (SPCZ) continues to lie farther south of the group in a disorganized formation as per satellite data. The afternoon ascent from Pago (14/00z) indicates a dry and stable atmosphere with a deepening easterlies through the mid-levels. MIMIC Total Precipitable Water (TPW) imagery also reflects a dry airmass advection over the region, with abundant moisture lying further west and north. Additionally, the sounding indices suggest the unlikelihood of localised thunderstorm activity within the nowcast period. Upper data shows a weak vorticity environment over the group with a strong deep-layer wind shear. Strong southwesterly winds persist at the upper levels, with a significant negative vorticity environment, inducing subsidence aloft that continues to suppress convective development. For tonight, expect partly cloudy skies with a few showers possible in some areas.
FRIDAY THROUGH WEDNESDAY:
Global weather models suggest that the easterly winds will dominate the surface, weakening through at least Saturday. A light to gentle and variable steering flow may persist through at least Monday, becoming northwesterly in the remaining days of this outlook. In addition, an intense high-pressure system sitting over the Tasman Sea is expected to move eastward, pushing the SPCZ to reside near south of Samoa by Sunday and is likely to extend showery conditions. This synoptic weather pattern may also direct strong southeasterly winds that may be restricted to the south of the group from Sunday. In addition, a low-pressure system may develop south of Samoa by Tuesday, causing winds to veer north to northwesterly through the remainder of this outlook period. The strong southwesterly to westerly winds aloft is forecast to persist at the uppers, suggesting a lack of significant upper-level forcing for convective enhancement.
MARINE OUTLOOK:
The latest marine observations from Aunu’u and King Poloa wave buoys, as well as altimeter data indicate that wave heights continue to fluctuate near 2 metres. In addition, an intense high-pressure system centred west of New Zealand is expected to gradually move eastward and direct high combined waves and swells by Sunday across the southern marine waters of Samoa. This wave activity is expected to coincide with the highest tide of May on Sunday, causing wave heights to exceed the advisory threshold of 2.5 metres. Therefore, a Marine Advisory may be enforced for southern marine waters within the next 12 – 24 hours; but for now, information is issued for precautionary measures.
ADVISORIES/WARNINGS:
NONE
Weather Duty Team:
F. Kalapani, S. Kalolo, S. Maualaivao & F. U. Namulau’ulu.