FORECAST DISCUSSION

SATURDAY 18thAPRIL 2026 – A.M SHIFT

TODAY:

Generally, the weak South Pacific Convergence Zone (SPCZ) is positioned over Samoa, inducing a line of instability that extends across the Fiji group and Vanuatu. The dominance of high-pressure systems at mid-levels and upper-levels of the atmosphere, as well as the lack of a climate driver (MJO), continues to suppress significant development of the SPCZ. The morning ascent from Pago (17/12z) indicates sufficient convective potential energy with a fairly moist vertical profile, and precipitable water reaching 52mm. Upper data also reveal a weak vorticity environment over the region with a strong deep-layer wind shear. These atmospheric conditions suggest the likelihood of localised thunderstorms today, although cloudy periods during the morning may result in late afternoon convection, particularly over interior highlands. Therefore, expect cloudy periods with some showers today, brief moderate falls and a few thunderstorms possible in the afternoon over highland areas.

SUNDAY THROUGH FRIDAY:

A high-pressure system currently centred east of Australia is expected to move eastward, forcing the South Pacific Convergence Zone (SPCZ) eastward and away from the group. This synoptic weather pattern may allow the easterly trade wind regime to predominate throughout the week. At mid-levels, a high-pressure ridge may linger over the region during this outlook period, providing light steering flow, which suggests a lack of vertical disruption to convective development. In addition, westerly to southwesterly winds aloft are forecast to dominate the uppers through at least Monday, before an upper high develops over the region. Models also hinted a weak short-wave trough embedded along the easterly flow on Tuesday and Wednesday, which may bring some showery conditions across the group.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King Poloa wave buoys as well as altimeter data indicate that wave heights have fluctuated below 2 metres over the past 24 hours. These wave activities are forecast to persist throughout this outlook period, posing no significant wave-related hazards to the islands’ marine waters.

ADVISORIES/WARNINGS:

NONE

Weather Duty Team:

F. Kalapani, S. Kalolo, S. Tavana & S. Maualaivao.