SYNOPTIC DISCUSSION
THURSDAY 26th MARCH 2026 PM SHIFT

TONIGHT INTO TOMORROW:

Current streamline analysis and pressure charts collectively agreed, illustrated that an elongated trough of low pressure system remains within the country, maintain unstable atmospheric conditions regardless of sunny breaks. What’s more, the sounding profile depicted continuous inflow of present moisture content from the surface through the 500 hPa pressure level, weakening wind strength at the surface-to-mid level, a mid-tropospheric dry slot, and a moderate instability. Further, a (850-700) hPa relative vorticity field still progress of revealing negative cyclonic signatures, stating the system’s extension and structure which support vertical cloud growth. In addition, present weak steering wind flow, and upper level southerly aloft, that correspond to strong wind shear environment over Samoa as a upper trough of low pressure lingers to the north. Therefore, a various satellite channels captured several isolated convective clouds with brief heavy downpours and a few thunderstorms which Afiamalu station recorded a peak value of 10.4 mm in 5 minutes at early afternoon. The atmosphere is unstable, evening through the nighttime with dominant of mid-upper clouds. Henceforth, the Heavy Rain Advisory remains enforced for all land areas. In a general sense the model consensus, suggest the severe system linger over the forecast region, that would maintain instability that suitable for deep convections with possible heavy falls and thunderstorms in some areas. Expect weak steering winds with prevailing upper southerly winds with the likelihood of lack upper level mechanism.

SATURDAY THROUGH WEDNESDAY:

Principally the model consensus, agreed that the severe weather system may slightly relocated near south of the area of concern, as a predicted ridging gradually strengthen in north, causing the mean wind flow to be northwest-to-west on Saturday. This expected synoptic setting, the dominated wind field slowly increase becoming moderate-to-fresh on Sunday through the later part of the new week. With this, confidently evince a likely formed convergence zone associated with the trough of low pressure, maintaining heavy downpours, thunderstorms and gustiness. In the upper atmosphere, the southerly winds will swerve from the southwest with winds diverge in directions signifying a divergence aloft, as a upper trough of low pressure propagated from the south over the Samoa region, which may maintaining deteriorate weather condition. So, there’s a low-to-moderate chance of severity that would affect the forecast area. Thus, we’ll continue to monitor and advise accordingly.

MARINE OUTLOOK:

Broadly, all marine observational data still indicates that wave and swell heights across Samoa’s water areas, fluctuate 1.5-2.0 metres. This wave trend is predicted to persist throughout the outlook periods based on the global wave models.

ADVISORIES/WARNINGS:
VALID: HEAVY RAIN ADVISORY

Weather Duty Team:
A. Liu, L. I. Tuatipi, C. Baker, & F. U. Namulau’ulu.