Updated

Updated · Yale Climate Connections · Sep 21

Hurricane Polo May Hit 160 Mph as Record-Warm Pacific Waters Fuel Category 5 Risk

Updated

Updated · Yale Climate Connections · Sep 21

Hurricane Polo May Hit 160 Mph as Record-Warm Pacific Waters Fuel Category 5 Risk

Q: Despite El Niño's suppression, what hidden trigger could suddenly awaken the unusually quiet Atlantic hurricane season?

The likeliest hidden trigger is the Atlantic’s African easterly wave train. Even under El Niño, those westward-moving disturbances coming off Africa can quickly seed storms if the hostile background pattern eases even briefly. That is why forecasters warn the basin could “wake up” fast despite its current quiet stretch. The Atlantic has been suppressed by El Niño-driven wind shear, dry air, Saharan dust and an unfavorable upper-level pattern. But the searched reporting notes that the wave train is already “fully operational” and showing healthy convective structure. In other words, the raw ingredients for storm formation are still moving across the tropical Atlantic. If moisture increases and vertical wind shear relaxes for a few days, one or more of those waves could organize rapidly over the still-warm Atlantic waters. Warm water alone has not been enough so far, but it remains a major fuel source waiting for better atmospheric conditions. Meteorologists also point out that Atlantic development this time of year can come from “homegrown” systems closer to land, especially near the Gulf or Southeast coast, where very warm water can help a weakening front or broad low-pressure area spin up. So the Atlantic’s quiet season is not necessarily safe; it is more accurately on hold. In short, El Niño is suppressing the basin, but a well-timed African wave — or a nearby homegrown disturbance — could abruptly break the lull if shear and dry air temporarily back off.

Q: How might the full moon amplify the impending East Coast nor'easter into a catastrophic coastal flooding event?

The full moon could significantly worsen flooding, but whether it becomes catastrophic depends on the nor’easter’s exact track, strength and timing with high tide. Around a full moon, the sun, Earth and moon align in a way that produces spring tides, often called king tides when seasonal water levels are already elevated. That means the normal high tide starts from a higher baseline than usual. If the nor’easter’s strongest onshore winds and lowest pressure arrive near those peak tides, the storm surge and wave-driven water pileup ride on top of an already elevated ocean level. That stacking effect is especially dangerous in places like the Chesapeake Bay, back bays, inlets and low-lying coastal roads from North Carolina to New England. Persistent easterly or northeasterly winds can trap water over several tide cycles, preventing it from draining fully at low tide. As a result, each successive high tide can flood farther inland. Forecasters are concerned not just about one high tide, but multiple rounds of high water. With offshore waves potentially reaching 15 to 18 feet and strong onshore winds continuing for days, beach erosion, dune damage and ocean overwash can intensify flooding even without a direct landfall. So the full moon does not create the storm, but it can raise the starting water level enough that a moderate coastal flooding event becomes major, and in the worst-case track scenario, potentially catastrophic in the most vulnerable coastal areas.

3 articles · Updated · Yale Climate Connections · Sep 21

National Hurricane Center forecasts Polo to strengthen from 65 mph Monday to 160 mph by midday Wednesday, potentially reaching Category 5 south of Mexico’s Pacific coast.
31°C waters, light 5-10 knot wind shear and a moist atmosphere are creating near-ideal conditions for rapid intensification; the SHIPS model puts Polo’s odds of becoming a major hurricane at 84% by Wednesday.
A tropical storm watch is in effect from Tecpan de Galeana to Punta San Telmo, and forecasts show Polo looping offshore before turning northwest and passing close to the coast on Thursday.
Longer-range models suggest Polo could send moisture into Baja California, northwest Mexico and the U.S. Southwest, with New Mexico facing 1-2 inches of rain and localized 3-5 inch flash-flood totals by midweek.