SYNOPTIC DISCUSSION

SATURDAY 04th APRIL 2026 PM SHIFT

TONIGHT & TOMORROW:

A weak trough of low pressure, extending from Tropical Disturbance 11F [TD11F], lies to the north of Samoa. A moist easterly wind flow also remains prevalent over the group. Recent observations indicate an increase in cloud cover. Associated moisture is gathering to the west of the islands. Sound observations have shown that instability is more pronounced over the area, with these activities near Samoa’s AOR. This system is anticipated to be the main weather driver for tonight and tomorrow. As a result, expect periods of cloudiness with isolated showers and moderate falls.

MONDAY THROUGH SATURDAY:

The Tropical Disturbance (TD11F), embedded within the active SPCZ, is expected to move southeastward as the strengthening ridge from the east aids its progression. Model guidance from both the ECMWF and GFS ensembles supports this scenario, with the majority of ensemble members showing a southeastward track. There is low confidence of showery and thundery activity over the island chain, as indicated by significant spread among ensemble solutions and limited agreement on convective intensity. For Monday through Friday, both the deterministic and ensemble model outputs forecast no significant synoptic systems affecting Samoa. The named ridge of high pressure will become the dominant weather feature. Trade wind weather patterns will continue, with diurnal atmospheric conditions largely responsible for any isolated showers and possible thunderstorms. Confidence in these details is moderate, given the general model consensus, but there is some uncertainty about shower coverage.

Tropical Disturbance 11F [TD11F] –

Although this system has no direct impact on Samoa, due to its closeness to our area, associated activities remain heavily influenced, for example, the extension of the trough of low pressure, associated with a surface convergence zone, which provides periods of cloudiness with isolated showers. Moreover, RSMC Nadi’s update as of April 04 0858UTC - TD11F’s central pressure at 999hPa, being analysed at 12.4S, 171.3E at April 04 0600UTC - and potential for this system to develop into a Tropical Cyclone in the next 24 hours is LOW. However, recent satellite data indicate lower-level cloud content wrapping into the low-level circulation, with wind observations in the system’s vicinity at 20 - 25 knots.

MARINE OUTLOOK:

Currently, marine observations from King Poloa, Aunu’u wave buoys, and altimeter data show wave and swell heights below 2 metres. There is no imminent threat to Samoa’s marine waters. Global wave models indicate wave activity will stay below the 2.5-metre advisory threshold.

ADVISORIES/WARNINGS:

NONE

Weather Duty Team:

MJS, Andrew Sofeni, Siala Maualaivao & Ne’emiaTutasi