SYNOPTIC DISCUSSION
MONDAY 30th MARCH 2026 AM SHIFT
TODAY:
A broad area of low-pressure system embedded within the South Pacific Convergence Zone (SPCZ) continues to lie over Samoa, triggering periods of heavy downpours and thunderstorms across the group. Satellite data indicate a line of deep convection just north of Samoa, with an upper trough overhead, sustaining and enhancing the development and growth of convective storms. The morning ascent from Pago (29/12z) shows moderate instability with a moist vertical profile where precipitable water reaches 61.13mm. MIMIC Total Precipitable Water (TPW) imagery reveals abundant moisture advection over the region as the moist northwesterly flow persists. Relative fields at 850mb and 700mb indicate strong vorticity signals over the forecast area, revealing the position of the SPCZ. However, satellite data indicate that active convection tends to concentrate just north of Samoa, where the convergence zone of the SPCZ is positioned. The weather system is expected to keep moist and unstable weather conditions over Samoa today, and may induce scattered showers, heavy at times, with gusty winds and thunderstorms. This maintains a high risk of flooding in rivers and low-lying vulnerable areas.
TUESDAY THROUGH SUNDAY:
Global weather models suggest that the South Pacific Convergence Zone (SPCZ) will remain stationary just north of Samoa through Tuesday, then move over the group by Wednesday. This synoptic weather pattern may maintain unsettling weather conditions over Samoa with the potential for heavy downpours 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 range from 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 Tuesday, 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, S. Kalolo, A. Sofeni & S. Tavanā