SYNOPTIC DISCUSSION
TUESDAY 02nd JULY 2025 AM SHIFT
TODAY:
The southeasterly trades continue to prevail across Samoa, advecting cool and dry airmass over the forecast zone. Satellite data over the past 24 hours indicate suppressed convective development, with mostly clear skies observed over the region. The ascent from Pago Pago this morning [12z], depicts a stable and dry atmosphere where available is mainly exists at low to mid-levels. This may allow cloud development and growth, particularly during the afternoon over the interior highlands, but may cut off at around 700mb as a strong temperature inversion exists there. The establishment of an upper ridge of high-pressure over Samoa contributes in dry and non-conducive environment for convective storm development. Therefore, fine weather today, apart from showers over highland areas.
WEDNESDAY THROUGH MONDAY:
Global weather models suggest that the high-pressure system centred west of New Zealand will steadily progress eastward and likely to relocate south of Tonga or east of New Zealand. This weather pattern will direct southeasterly winds that may exceed the wind strength of 20 knots on Wednesday into Saturday, but mostly concentrated in the southern-facing shores of the Samoan group. Then, eventually decreased likely by Sunday as the high-pressure continues to move further eastward. In addition, the strong southwest to southerly is expected to dominate the uppers, advecting that polar descending airmass across the group, which may continue to suppress convective storm development and growth.
MARINE OUTLOOK:
An intensified high-pressure system to the west of New Zealand is aiding the generation and development of large waves and swell activities. A fetch area, concentrated near the Fiji Islands, is anticipated to affect Samoa’s land areas later on Friday. Furthermore, the same system is expected to generate large waves and swells that will impact coastal and open waters, possibly by tomorrow evening at the latest. Meanwhile, the latest observations have indicated a slight increase in wave activity, now ranging from 2 to 2.5 metres. Therefore, the group is likely to expect the likelihood of a Marine Advisory to be activated in the next 12 to 24 hours.
ADVISORIES/WARNINGS:
NONE
Weather On-Duty Team:
MJS, F. Kalapani, P. Huch & A. Uili.