re: Hurricane/Tropical Storm Idalia Discussion Thread

Dr. Levi Cowan
@TropicalTidbits
As we enter the peak weeks of the Atlantic hurricane season, it will be interesting to see where genesis events are produced. Sometimes, El Nino's suppressive influence on the Caribbean leads to a northward shift in the favorable zone.

In a year when the Gulf of Mexico + west Atlantic warm pool is much warmer than normal, patterns such as this one in Week 2 ensemble forecasts can increase risks for genesis close to North America. Strong anticyclonic wave breaking at 200mb can lead to low to mid-level vorticity perturbations (such as from weak frontal boundaries or cutoff lows) being injected south of 30N, where warm water and deep moisture can lead to so-called "homegrown" TC genesis. Sometimes African easterly waves arrive from the east as an additional source of vorticity and moisture.

The plots of 200mb and 850mb zonal wind anomaly from the ECMWF ensemble below show an overlap of anticyclonic wave breaking over anomalous vorticity at the surface across the western Atlantic and Gulf of Mexico, which will be something to keep an eye on in late August.