SYNOPTIC DISCUSSION
TUESDAY 24th JUNE 2025 AMSHIFT
TODAY:
The moderate easterly winds prevailing over the island group are associated with periods of cloudiness and some isolated showers observed this morning. The strong trade wind conditions confine the SPCZ to the western side of the forecast area, as indicated by the latest satellite imagery, and inhibit severe convection within our area of responsibility. A slight amount of moisture is present at the lower levels of the atmosphere, as depicted by the Pago Pago sounding profile of this morning [12Z], which correlates with the MIMIC-TPW animation showing marginal moisture levels varying between 50 and 60 mm. Additionally, the persistence of a strong wind shear environment, coupled with significant upper divergence, sustains conditions to the west of the country. In contrast, the aforementioned wind patterns restrict the vertical development of broad convective activities over the Samoan group. CIMMS observations indicate the presence of upper convergence, which contributes to the short-lived cloudiness over the group, despite the slight topographical lifting available. Furthermore, it is expected that the same weather conditions will prevail in the afternoon, leading to anticipated cloudy periods with some isolated showers and a few thunderstorms.
WEDNESDAY THROUGH MONDAY:
The global weather models indicate a gradual rise in rainfall activity from early Wednesday until early Saturday, despite some uncertainties. The anticipated scattered showers, which may include heavy downpours, are expected as a trough of a low-pressure system traverses the area of responsibility. This system is likely to remain over Samoa until Thursday and may continue to advance through Saturday, bringing potential periods of heavy rainfall across the group. The steering winds are expected to become light and variable from late Wednesday through at least Saturday, resulting in weak low-level wind shear that is conducive to vertical growth. Additionally, an upper trough projected to move in from the west is expected to settle over Fiji by Wednesday, subsequently affecting Samoa, which may trigger upper divergence through Thursday, thereby enhancing the surface system. Moreover, conditions are anticipated to ease by late Saturday, towards the conclusion of the outlook period, due to the likely dominance of a light to gentle trade wind regime.
MARINE OUTLOOK:
The Marine Advisory remains valid for all marine waters of Samoa today. This is attributed to a high-pressure system located further southeast of the group, which continues to produce waves and swells exceeding 2.5 meters, accompanied by easterly winds that affect our marine waters. Nevertheless, recent marine observations suggest a gradual decrease in wave and swell heights, falling below 2.5 meters later today.
ADVISORIES/WARNINGS:
MARINE ADVISORY – ALL OF SAMOA
Weather On-Duty Team:
Gospel. Niko, Andrew. Sofeni, Fuimaono Uili Namulau’ulu & Ne’emia. Tutasi