SYNOPTIC DISCUSSION

THURSDAY 02nd APRIL 2026 PM SHIFT

TONIGHT:

The South Pacific Convergence Zone (SPCZ), which affected Samoa over the past few days, continues to move southward, resulting in improving weather conditions across the group. Satellite data indicate deep convection to the south with a few patches of fair-weather low-level clouds streaming towards the group. The afternoon ascent from Pago (02/00z) reveals a weak atmospheric instability with a fairly moist vertical profile where precipitable water reaches 50.86mm. A deepening northerly winds through the ~500mb keeps a moist equatorial flow over the region. Relative vorticity fields at 850mb and 700mb indicate counterclockwise motion over the forecast area, which is not conducive to storm development synoptically, suggesting the domination of high-pressure systems. In addition, a strong upper divergence area remains to the south of Samoa, where convection of the SPCZ is located. This weather system is expected to maintain its southward movement away from Samoa, thus warranting the cancellation of the Heavy Rain and Flood Advisories for all land areas. However, a moist northerly wind flow prevails over the group, which may bring showery conditions with the potential for moderate falls in some areas tonight; otherwise, conditions will be mostly fine in most areas.

FRIDAY THROUGH WEDNESDAY:

Global weather models indicate that minimal precipitation is expected throughout this outlook period, apart from Saturday when a low-pressure trough moves across Samoa. Showery conditions are expected during this period with localised afternoon convection, which may bring moderate to heavy showers across highland areas. The lack of a significant mid to upper level forcing suggests that cloud development will be largely diurnally driven throughout this outlook period. In addition, model consensus picks up a low-pressure system currently centred northeast of Fiji and moves it to the east of Vanuatu while deepening. This weather system may further intensify through the new week as it tracks through the south of Fiji. This weather system is not expected to directly affect Samoa as per the latest model runs.

MARINE OUTLOOK:

The latest marine observations from King Poloa and Aunu’u wave buoys, as well as altimeter data, generally indicate that wave and swell heights fluctuate below 2 metres, which shows 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:

CANCELLED: HEAVY RAIN ADVISORY

CANCELLED: FLOOD ADVISORY

Weather Duty Team:

F. Kalapani, S. Kalolo, A. Uili & S. Maualaivao.