FORECAST DISCUSSION
TUESDAY 12th MAY 2026 AMSHIFT
TODAY:
The South Pacific Convergence Zone (SPCZ) continues to lie south of Samoa in a disorganized formation with deep convection over the Solomon Islands. Meanwhile, an easterly wind flow prevails across Samoa at the surface with an embedded speed convergence just south of the group. The morning ascent from Pago (11/12z) indicates a conditionally unstable atmosphere with a precipitable water value reaching 47.60mm, which will support localised afternoon thunderstorms over the interior highlands. MIMIC Total Precipitable Water (TPW) imagery well reflects this moisture advection as the deepening easterlies persist. In addition, upper data reveal a weak vorticity environment over the forecast area with a strong deep-layer wind shear, suggesting that convective storms may be short-lived today. Therefore, showery activity is expected over the highlands and parts of the southern areas during the afternoon, with a few thunderstorms possible.
WEDNESDAY THROUGH MONDAY:
Global weather models suggest that the easterly winds will dominate the surface throughout this outlook period with minimal showers and typical localised afternoon convection. High-pressure area may generally dominate the mid-levels through at least Friday, resulting in weak variable steering flow during this period. In addition, an intense high-pressure system sitting over the Tasman Sea is expected to move eastward, pushing the SPCZ to reside just south of Samoa by Sunday and inducing rainfall activities. This synoptic weather pattern may direct strong southeasterly winds across the south of the group by Sunday, while a mid-level trough gradually builds over the forecast area. The strong southwesterly to westerly winds aloft is forecast to persist at the uppers during this outlook period, suggesting a lack of significant upper-level forcing for convective enhancement.
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. However, a southeasterly swell event is anticipated to enter our southern seas by the end of the week as an intense high-pressure system stationed over the Tasman Sea advances eastward. JMA predictions are hinting at a 30% chance of elevated swells and waves of more than 3 metres during this period and may prompt the issuance of a marine advisory if wave models persist in the next 2-3 days.
ADVISORIES/WARNINGS:
NONE
Weather Duty Team:
Kalapani, Niko, Namulau’ulu & Maualaivao.