SYNOPTIC DISCUSSION

TUESDAY 31stMARCH 2026 PM SHIFT

TONIGHT INTO TOMORROW:

Samoa continues to experienced unstable weather, that brought moist and cloudy conditions, generated periods of rain with brief heavy downpours, a few thunderstorms and gusty winds during rain mainly over windward locations and elevated regions in both islands. These severe weather patterns was primarily caused by the elongated active trough of low pressure still embedded within the South Pacific Convergence Zone (SPCZ) which remains within the vicinity. The vertical structure of the atmosphere, based on the sounding profile, basically indicated abundant moisture at the lower troposphere, present mid-to-upper level dry slot, deepening north-to-northwest wind flow and weak instability. On that note, the (850-700) hPa still depicted moderate-to-strong signature of cyclonic rotation, a clear hint of an existed surface lifting mechanisms. But, the wave vapor channel coincides with the weak upper divergence aloft since the upper trough of low pressure remains over the island chain, with weak wind shear, that would support vertical cloud growth tonight. Hence, the heavy rain and flooding warning was still enforced for all land areas. For tomorrow, the severe weather system is forecasted to descend to the southwest, that could maintain the prevailing wind flow to be more northerly, with wind strength becoming moderate with periods of gustiness. Yet, expect accumulated rainfall, and thunderstorms over the vicinity.

THURSDAY THROUGH MONDAY:

Principally, the model consensus suggested that the severe weather system would shift further southwest, as a ridge of high pressure to the southeast slowly strengthen on Thursday, which would sustain possible moderate-to-fresh northerly wind flow with gustiness. Then, the mean wind flow gradually becomes easterly on Friday as the previously stated ridge of high pressure move to the west, hinting the trade wind regime would become the dominant weather feature across the forecast area in the later part of the outlook period. 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:

Currently the marine observations from King Poloa and Aunu’u, as well as altimeter data, continues to revealed that the wave and swell heights fluctuated around 2 metres, which suggests no imminent threat across Samoa’s marine waters. Global wave models suggest that this 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:

A. Liu, A. Sofeni, P. Huch, & N. Tutasi.