West Pacific Heating Up?

The Northern Hemisphere tropical cyclone season is starting to wind up, and it looks like the first basin to take advantage may be the West Pacific. This could be a very active Typhoon season thanks to the developing El Niño event. Figure 1 shows the Google DeepMind TCs forecast over the next two weeks, showing a fairly robust signal for a TC to form between Guam and the Philippines.

There is a lot of spread in track and intensity at this range, and TC formation is not guaranteed, though it makes some sense with the Madden Julian Oscillation (MJO) moving across the region. Other models also show some development, though it’s mostly in the Day 9-10 range right now (Figures 2-3).

The environment looks marginal for development. It looks like a tropical upper tropospheric trough (TUTT) will be draped across the West Pacific, but if it cuts off and a ridge builds overhead, the upper-level winds could become more favorable for development (Figure 4).

On some models, however, the TUTT takes longer to cut off, and with more troughing over the West Pacific (Figure 5), TC development is delayed. This process of eroding the TUTT involves a lot of “diabatic heating” produced by convection, a process that can be difficult to model. So I will be curious to see how AI models handle this evolution.

Regardless of development, it looks like this MJO passage will be associated with another period of westerly winds or reduced trades across the equatorial Pacific, helping to amplify the developing El Niño event (Figure 6).

As the MJO pulse progresses eastward, we could see development in the East Pacific towards the start of June, and of course we’ll have to watch the Caribbean and Gulf for early-season development as well.