SYNOPTIC DISCUSSION
FRIDAY 10thAPRIL 2026 AM SHIFT
TODAY:
A ridge of high-pressure continues to dominate Samoa, maintaining genrally fair weather conditions while keeping deep convection to the south of the group. Satellite data shows mostly cloud-free conditions over the forecast area, with occasional thunderstorms and rain confined to the south, where the SPCZ is currently located. The morning ascent from Pago (09/12z) indicates moderate atmospheric instability, a fairly dry vertical profile and precipitable water reaching 60.70mm. The movement of Tropical Cyclone Vaianu towards the north of New Zealand is channelling moisture advection across Samoa as depicted by MIMIC Total Precipitable Water (TPW) imagery. Relative vorticity fields at 700mb and 850mb indicate a weak vorticity environment over the forecast area. In addition, high-pressure systems dominate the mid through upper-level atmosphere over the region, which induces subsidence aloft and a weak deep-layer wind shear environment. For today, mostly fine weather is expected, apart from few afternoon thunderstorms particularly over highland areas.
SATURDAY THROUGH THURSDAY:
Global weather models suggest that the easterly trade winds will predominate Samoa throughout this outlook period, with series of short-wave troughs that passes across the group. This synoptic pattern may induce showery conditions over the forecast area, with the potential for moderate to heavy falls in some areas starting from Saturday. The easterly steering flow is forecast to be gentle to moderate during this period, suggesting a lack of vertical disruption to convective storm development and growth. In addition, an upper trough approaching from the west is expected to lie near Fiji by Sunday, bringing upper diffluence that may enhance cloud development through at least Wednesday of the new week. This upper level system is forecast to exit through the north by late Wednesday while dissipating.
MARINE OUTLOOK:
The latest marine observations from King Poloa and Aunu’u wave buoys, as well as altimeter data indicate that wave and swell heights are fluctuating around 2 metres over the past 24 hours. Global wave models indicate that wave activity may slightly exceed 2.5 metres over the southern marine waters of Samoa from Saturday through at least Monday of the new week. During this period, there is a low probability of significant wave heights entering the northern marine waters during this outlook period.
ADVISORIES/WARNINGS:
NONE
Weather Duty Team:
F. Kalapani, A. Niko, P. Huch & U. Namulau’ulu.