Sting Jet or No Sting Jet & Simon and Trudy Give Forecasters Fits in the Pacific

The El Niño-driven band of upper-level winds stretches from the Gulf to the Caribbean to Africa. We still can't rule out a system developing in a random pocket of slightly supportive atmosphere outside of the band before this hurricane season ends, however, so we'll continue to watch.

For now, no tropical development is expected for the foreseeable future.

A comment about Hurricane Isaias: a lot has been said about what caused the band of strong winds over the western Florida Panhandle. You've probably heard the term "sting jet" floated around. A sting jet normally occurs in systems transitioning to non-tropical storms heading in a general west-to-east direction. The band of strong winds – the sting jet – occurs on the back-right quadrant of the storm when dry air suddenly forces strong winds above the surface down to ocean or ground level.

No doubt something similar happened during Isaias's landfall, but these strong winds occurred in a different part of the storm – the back-left quadrant.

Descending air was clearly involved in the phenomenon. Suddenly the temperatures warmed and the winds gusted like a sudden Santa Ana in California or Chinook in Colorado. Air compresses as it moves to higher pressure, like an old-fashioned bicycle pump gets warm as you compress the air to blow up tires.

Almost certainly, high-speed air was descending on the left side of the storm as dry air was wrapping in. Also, there can be an acceleration of the air near the coast due to the land slowing the air's movement while it speeds by over the water.

My bottom line is that it was a sting-jet-like phenomenon, but it doesn't quite fit into the typical sting jet bucket because it occurred in the wrong part of the circulation.

NOAA's high-resolution hurricane model showed the band of extra-strong wind on the west side of the storm. That model can be picked apart to understand where exactly in the atmosphere the strong winds came from and what triggered them. There was, for example, a strong upper-level disturbance just to the west, which was propelling Isaias north.

In the end, the gusts from the band of extra-strong gusts were within what is expected in a 105-mph hurricane, but the exact meteorology that generated them is an open question.

IN THE PACIFIC NEAR MEXICO

Tiny Hurricane Simon is loitering well south of Cabo San Lucas, offshore of west-central Mexico. Steering currents have collapsed, so the future track is uncertain, but Cabo is going to have to watch it. The highly uncertain forecast eventually takes the storm that way, although it's forecast to be weakening on the trip north.

As always, forecasts for storms caught in pockets of atmosphere with no clear steering winds are subject to large errors and are likely to change. So far, Simon has been a poster child for this reality.

Simon's big sister, Hurricane Trudy, is offshore of southern Mexico. It's also defying forecasters. Again, the steering currents are expected to collapse on its track offshore or near the Mexican coast. Everyone in west-central Mexico needs to pay attention to the forecast.