SYNOPTIC DISCUSSION
WEDNESDAY 26th NOVEMBER 2025 AM SHIFT
TODAY:
The South Pacific Convergence Zone (SPCZ) remains further south and west of Samoa in a fairly active state, affecting the regions of Fiji, Tonga and parts of Solomon Islands. Meanwhile, a moist northeasterly wind flow persists across Samoa with a southwesterly aloft that steers upper-level clouds and moisture over the group during the early morning. These weather patterns are reflected in streamline analysis and CIMSS data, with a high-pressure ridge over the region that keeps the SPCZ to the south. The morning ascent from Pago Pago (12z) reveals a fairly dry vertical profile with marginal instability and precipitable water value reaching 47.71mm. In addition, atmospheric data generally reveal the dominance of high-pressure ridges from mid to upper level atmosphere, which also results in a weak wind shear environment. Therefore, cloud development today will be largely diurnally driven, with mostly congestus development over the interior areas during the afternoon with a few possible thunderstorms. For today, expect partly cloudy skies with brief showers over the highlands and a few thunderstorms possible.
THURSDAY THROUGH TUESDAY:
Global weather models suggest that the SPCZ will gradually progress over Samoa by early Friday, as a high-pressure system builds over the southeast of New Caledonia. The weather system is forecast to bring occasional rain with a potential of heavy falls through Monday of the new week. The northwesterly to westerly winds are forecast to dominate the mid-levels during this period, aiding the eastward movement of the system towards Samoa. This movement of the weather system is expected to refine cross-equatorial moisture advection as the northerly to northwesterly dominates. In addition, an area of upper diffluence may linger over the forecast area from Friday, potentially enhancing convective storm growth and development during this period.
MARINE OUTLOOK:
The latest marine observations from Aunu’u and King-Poloa wave buoys as well as altimeter data, signify that wave heights remain below the advisory threshold of 2.5 metres. These wave conditions are is likely to persist through Saturday, with an approaching northerly long-period swell expected on Sunday with a low chance of impact. However, we’ll thoroughly monitor the system and update accordingly.
ADVISORIES/WARNINGS:
NONE
Weather Duty Team:
F. Kalapani, S. Kalolo, A. Uili & F. U. Namulau’ulu.