FORECAST DISCUSSION

WEDNESDAY 20thMAY 2026 AM SHIFT

TODAY INTO TONIGHT:

The satellite showcase, the South Pacific Convergence Zone (SPCZ) remains to the south of Samoa, with associated rainfall activities and a few thunderstorms, leading to a slight eased conditions today. However, the sounding profile and total precipitable water channel, both revealed sufficient low-level moisture content while slowly drifting to the south, dry slot and a weak convective inhibition that is represented through a inversion layer, where intense surface heating in the afternoon, required to overcome it. So, expect afternoon showers and short-lived thunderstorms, as the weak upper divergence aloft remains existed over the vicinity. As for tonight, model consensus generally agreed that the SPCZ is forecasted to continue to move southward, while an evolved low-level circulation formed, which leads to improving weather across Samoa. 

OUTLOOK: THURSDAY THROUGH TUESDAY

According to the current global weather guidance, that throughout this outlook period, anticipate mostly fine weather conditions apart from afternoon showers mainly over highlands and windward locations. This is because, the previously low-level circulation drifted further southeast, causes the mean wind flow to swerve northerly-to-northwesterly on Thursday, then westerly-to-southerly hinting a ridge of high pressure extends from the south, but the east of New Zealand, as it migrate further to the east on Friday. This weather feature will become dominate across the forecast region, which maintains the trade wind regime through the later part of the outlook period.

MARINE OUTLOOK:

This morning, the current marine observations across Samoa’s southern marine waters has been diminished below 2.5 meters due to the high pressure system to the east of New Zealand is expected to continues to move eastward, causing high combined wind waves and swells from the south of Samoa to subside. Henceforth, the above mentioned advisory is officially cancelled for the southern marine waters of Samoa. Based on global model wave models, generally forecasted that this wave trend will likely to persist throughout the outlook period. 

ADVISORIES AND WARNINGS:

VALID: HEAVY RAIN – ALL OF SAMOA

CANCELLED: MARINE ADVISORY – SOUTHERN MARINE WATERS

Weather Duty Team:

A. Liu, A. Niko, S. Maualaivao, & C. Baker.