SYNOPTIC DISCUSSION

TUESDAY 14thOCTOBER 2025 PM SHIFT

TONIGHT INTO TOMORROW:

The convergence zone that caused unsettling weather in Samoa yesterday has shifted north, resulting in improved weather conditions today. At the same time, a high-pressure system located northeast of New Zealand is generating moderate southeasterly winds over Samoa, which is bringing a cool and dry airmass to the region tonight while keeping the previously mentioned severe system to the north. The Pago Pago sounding profile [00Z] also shows a gradual decrease in moisture levels in the atmosphere compared to the over 55 mm of precipitable water recorded yesterday. This aligns with the MIMIC TPW animation, which highlights that the inducing moisture is now more concentrated to the north of the area of responsibility. The streamline analysis from regional weather charts further indicates that the aforementioned convergence has moved northward. The dry and stable conditions experienced across the group tonight are also due to the lack of upper divergence, combined with the ongoing strong wind shear environment. These conditions are expected to foster mostly fine weather through tomorrow, leading to the cancellation of heavy rain and flood advisories for all land areas. Consequently, partly cloudy skies with some brief showers in some areas are anticipated to continue tomorrow, along with the persistence of moderate southeasterly winds.

THURSDAY THROUGH MONDAY:

The weather forecast indicates that the convergence zone is expected to stay to the north until late Friday. Passing showers are anticipated starting Thursday due to the expected dominance of the easterly trade winds, likely reinforced by another high-pressure system extending from the south of New Caledonia. This ridge will also support the maintenance of the previously mentioned convergence zone to the north. The eastward progression of the highlighted high pressure is likely to strengthen the convergence zone to the north and may lead to its descent over the forecast area by Saturday, resulting in heavy rainfall. These severe weather conditions are expected to persist throughout the end of this outlook period. Additionally, an upper diffluence is projected to develop north of the islands by Saturday and may continue into the new week, potentially enhancing the aforementioned surface system.

MARINE OUTLOOK:

The latest marine observations indicate a decreasing trend of wave heights, well below the advisory threshold of 2.5 metres, and are expected to persist through this week. Therefore, marine advisory is also cancelled for all marine waters. The global wave models also forecast the persistence of wave heights of below 2.5 metres throughout this outlook period.

ADVISORIES/WARNINGS:

CANCELLED: HEAVY RAIN ADVISORY

CANCELLED: FLOOD ADVISORY

CANCELLED: MARINE ADVISORY

Weather Duty Team:
Gospel. Niko, Aquinas. Uili & Samuelu. Tavanā