SYNOPTIC DISCUSSION
MONDAY 09th MARCH 2026 PM SHIFT

TONIGHT:

Unstable atmospheric conditions persist over Samoa as a low-pressure trough lies to the south and west of the group with prevailing moist northeasterly winds. This weather setup brings about cloud periods with brief moderate to heavy showers in parts of the group over the past 24 hours. Satellite data this afternoon shows active convections just south and west of Samoa with patches of congestus clouds streaming along the wind flow towards the group. The afternoon ascent from Pago (09/00z) indicates strong instability with good precipitable water value reaching 58.10mm. The deepening easterlies at low-levels refine that moisture advection over the region which is well reflected on MIMIC Total Precipitable Water (TPW) imagery. In addition, CIMSS data indicates a weak low-level vorticity with a weak to moderate wind shear environment and lack of upper level forcing over the forecast area. These atmospheric data reveal favorable atmospheric conditions with the absence of significant surface uplift, resulting in easing periods across most areas of the group. For tonight, expect cloudy periods with some isolated showers, brief heavy falls in some areas and a few thunderstorms likely.

TUESDAY THROUGH SUNDAY:

Global weather models suggest that the easterly trade winds will dominate the forecast area through at least Saturday. Model consensus hints that the SPCZ may fluctuate further south of the group in a suppressed and disorganized formation throughout this outlook period. Speedconvergences along the easterlytrade winds are expected to induce showery conditions with gusty periods this week, although predominantly fine weather is expected across most areas. In addition, a weak short-wave trough is forecast to move across the group on Sunday and is likely to bring showery conditions at the end of this time frame. The lack of a significant upper-level forcing throughout this outlook period suggests that cloud development will be largely diurnally driven over the forecast area.

MARINE OUTLOOK:

The latest marine observations from Aunu’u, King Poloa wave buoys and altimeter data indicate that the wave and swell heights fluctuate below 2 meters, suggesting no imminent threat across Samoa’s marine waters. Global wave models suggest that wave activities will persist below the advisory threshold of 2.5 metres throughout this outlook period.

ADVISORIES/WARNINGS:
VALID: HEAVY RAIN ADVISORY

Weather Duty Team:
S. Gafa, F. Kalapani, A. Uili & S. Tavana.