SYNOPTIC DISCUSSION

TUESDAY 31stMARCH 2026 AM SHIFT

TODAY:

A broad area of low-pressure embedded within the South Pacific Convergence Zone (SPCZ) remains over Samoa, resulting in the development of low circulation near the group. Satellite data indicates associated convection to be concentrated to the north of the group, leading to easing weather conditions across the forecast area this morning. However, the morning ascent from Pago (30/12z) reveals a moist and unstable atmosphere where precipitable water reaches 62.44mm. Relative vorticity field at 850mb indicates good vorticity signal over the region as a result of the SPCZ. In addition, the axis of a weak upper trough lies over the forecast area, bringing a weak deep-layer wind shear environment and weak to moderate upper divergence. For today, expect isolated showers with brief heavy falls and thunderstorms, with gusty winds during heavy rain.

WEDNESDAY THROUGH MONDAY:

Global weather models suggest that the deep convection of the South Pacific Convergence Zone (SPCZ) to the north of Samoa will shift over the group by Wednesday. This synoptic weather pattern may maintain moist and unsettled weather conditions over Samoa, keeping the risk of intense heavy falls and thunderstorms during this period. The movement of the SPCZ over the group is expected to induce strengthening northerly winds on Wednesday. where wind speeds may reach 20-25 knots. By Friday, the trade wind weather regime is expected to predominate through the end of this outlook period, bringing improved weather conditions across the group. In addition, a weak upper trough may influence the group through at least Wednesday, and with the lack of a significant upper-level system, cloud development will be largely diurnally driven during the remainder of this outlook period.

MARINE OUTLOOK:

The latest marine observations from King Poloa and Aunu’u, as well as altimeter data, indicate that wave and swell heights continue to fluctuate around 2 metres, which suggests no imminent threat across Samoa’s marine waters. Global wave models suggest that wave activity will remain below the advisory threshold of 2.5 metres throughout this outlook period.

ADVISORIES/WARNINGS:

VALID: HEAVY RAIN WARNING

VALID: FLOOD WARNING

Weather Duty Team:

F. Kalapani, L. Tuatipi, A. Uili & S. Tavana.