FORECAST DISCUSSION

MONDAY 20thAPRIL 2026 – A.M SHIFT

TODAY:

The easterly trade wind regime continues to dominate the region, resulting in mostly fine weather across the group. Weather maps analysis and ASCAT data indicate that a high-pressure system centred further southeast remains the primary driver, directing gentle to moderate easterly winds along with the advection of fair-weather clouds. The morning ascent from Pago (19/12z) reveals sufficient convective potential energy and low-level moisture, with precipitable water reaching 49.29mm. Warm air advection (WAA) aloft is also evident in the profile, where veering winds (between 550mb and 200mb) indicate atmospheric instability, which is consistent with a CAPE value of 1707J/kg. In addition, high-pressure systems dominate the mid levels, promoting warm airmass advection over the forecast area. The lack of a significant upper level forcing over the region suggests that cloud development will be largely diurnally driven. For today, current atmospheric conditions support the development of few afternoon thunderstorms, particularly over interior highlands, which may bring brief moderate to heavy falls in localized areas; otherwise, mostly fine weather in most areas.

TUESDAY THROUGH SUNDAY:

Global weather models suggest that the easterly trade winds will predominate the region throughout this outlook period. An embedded weak short-wave trough at the surface may move across the group on Tuesday and is likely to bring some showery conditions. The trades may persist at gentle to moderate intensity throughout the week, with a fresh winds surge entering the forecast area by Saturday. In addition, high-pressure systems are forecast to dominate the mid and upper levels during this period, suggesting subsidence aloft, which may inhibit widespread significant convection over the region. Therefore, mostly fine weather conditions are expected across the group, apart from typical localized afternoon thunderstorms possible over interior highland areas.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King Poloa wave buoys, as well as altimeter data, indicate that wave heights continue to fluctuate well below 2 metres. 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, A. Sofeni, P. Huch & A. Uili.