FORECAST DISCUSSION

SATURDAY 02ndMAY 2026 AM SHIFT  

TONIGHT INTO TOMORROW:

A weak trough of low-pressure lies within the vicinity of Samoa, triggering a line of isolated congestus development across the group. The morning sounding indices from Pago (01/12z) indicate a favourable environment for convective storm development and growth. However, upper data reveal a weak vorticity environment over the forecast area, with a strong deep-layer wind shear, which significantly deters convective vertical growth. In addition, a high-pressure area dominates the mid-level atmosphere over the region, contributing to some dry airmass and subsidence aloft. The lack of a significant upper-level lifting suggests that convection will be largely diurnally driven. Therefore, expect cloudy periods with scattered showers, brief moderate to heavy falls in some areas and a few thunderstorms.

SUNDAY THROUGH FRIDAY:

Global weather models suggest that the aforementioned trough of low-pressure will linger over the group, bringing cloudy periods and showery conditions through at least Sunday, with the potential for moderate to heavy falls in some areas. In addition, the South Pacific Convergence Zone (SPCZ) may reside near south of Samoa during the new week, and is likely to extend rainfall activities over the group with periods of possible isolated heavy downpours. The steering flow during this period is expected to remain light to gentle, suggesting the lack of vertical disruption in cloud development. Additionally, strong southwest to westerly winds aloft may persist over the region, and the lack of a significant upper-level forcing suggests that convective storms will be largely diurnally driven during this period.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King Poloa wave buoys indicate that wave heights continue to fluctuate below the advisory threshold of 2.5 metres. Global wave models suggest that a southerly combined wind waves and swells may approach the group and likely affect the southern marine waters from Wednesday. These wave activities may exceed the advisory threshold during this period.

ADVISORIES/WARNINGS:

NONE

Weather Duty Team:

F. Kalapani, S. Kalolo, C. Baker & F. U. Namulau’ulu.