Maila Moves Towards Papua New Guinea, 90W Threatens the Mariana Islands

The period of increased TC activity across the Northwest and Southwest Pacific continues, with 3 systems of note today. First, Vaianu is weakening and transitioning to an extatropical cyclone, though it could bring some impacts to the Northern Coast of New Zealand (Figure 1).

Further west, Maila is located over the Solomon Sea, and looks poised for a rare pass near the southeast tip of Papua New Guinea (Figure 1). The TC is currently weakening due to a combination of some easterly shear and upwelling of cooler waters, and right now models still keep it fairly weak to the North of Australia (Figure 2).

Regardless of the exact intensity, however, Maila will continue to be a slow-moving flood threat in the region, dropping copious amounts of rainfall (Figure 3) in an area that does not see a ton of impacts from strong tropical cyclones.

Turning our attention to the North side of the equator, Invest 90W is getting organized. The system is forecast to become a TC and intensify in an environment of favorable upper-level winds as it moves off to the Northwest (Figure 4).

One of the key forecast questions is whether 90W will pass over, to the east, or to the west of the Mariana Islands. Right now AI models are generally further east than physics-based models, though there is considerable ensemble spread (Figure 1). A lot of the forecast uncertainty seems to be related to the strength of a narrow ridge to the north of the TC and how much that is able to steer the system to the west (Figure 5).

As discussed previously, the twin (triplets technically) TCs in the West Pacific are helping to enhance a very strong westerly wind burst (WWB) across the region (Figure 6). This month’s climate model forecasts are generally trending even stronger with the likely El Niño later this month, probably in response to this equatorial forcing.