Hurricane Ida has unleashed her wrath on New Orleans and the Gulf Coast, and is now moving further inland as a tropical depression after making landfall as the fifth most-powerful tropical storm in U.S. history.
The outer bands of rainfall have reached southwestern Tennessee, and will continue to spread north and east over the next 24 hours before finally reaching the northern Cumberland Plateau region. The National Weather Service has expanded a Flash Flood Watch that was in place for the western half of Tennessee to include the plateau and all of East Tennessee with the exception of the mountains.
The expanded flood watch comes as the NWS has actually lowered total rainfall amounts for the northern plateau, now forecasting our region to receive 2 to 3 inches of rain by the time things taper off on Wednesday. At this time Sunday, the forecast was for 3 to 4 inches of rain.
The revised forecast comes as the GFS model actually enhances rainfall projections across our region, now showing up to 5 inches of total rain accumulation. But most other models are showing decreased rainfall totals, and the higher-resolution NAM model in particular is showing rain bands diminishing as they reach the northern plateau.
Timing: Rain will begin late tonight, as Ida moves inland at an even faster speed than was predicted. By daybreak tomorrow, rain will likely have overspread the entire region. That could place Tuesday night sporting events in jeopardy.
The duration of precipitation will be relatively short-lived, as tropical systems go. By daybreak on Wednesday, the rain will be starting to taper off. By late morning Wednesday, it’s likely that the rain will be finished completely.
Main Impacts: The primary impact will be the rainfall, though widespread flooding seems unlikely. Isolated flash flooding will be the biggest concern, and could occur if and wherever heavier downpours set up. There’s also a very low risk for severe weather, specifically, isolated tornadoes. This risk is primarily to our south, nearer the Georgia and Alabama borders. The Storm Prediction Center has not highlighted a risk area for severe weather this far north.
Temperatures: A secondary impact of Ida will be cooler temperatures. The high temperature on Tuesday likely won’t get much above 70°, with persistent rain showers throughout the day. The high temperature on Wednesday should be in the 70s as well. It might be Friday before we’re back to near 80°. With the moist tropical atmosphere in place, nighttime temps will still be warm and we’ll be quite humid. But as the tropical system departs, dew points will drop and nighttime temps should be in the 50s by the end of the week. Friday looks absolutely spectacular, with lots of sunshine and low relative humidity.
Further tropical development: Tropical Storm Kate is currently spinning way out in The Atlantic. But she’s moving almost due north and should remain far away from the U.S. mainland, making her what weather enthusiasts refer to as a “fish storm” — which is to say, a storm that only the fish experience.
However, there’s a wave that’s peeling off the coast of Africa that already has the National Hurricane Center’s attention, and it’s likely to develop into a tropical cyclone very quickly. We’re moving into the Cape Verde season, named for the Cape Verde islands off the African coast. This is the region in which some of our strongest hurricanes here in the U.S. develop, and any wave that peels off the African coast has to be monitored closely. For now, there’s no reason to think that this storm will make it to the U.S. mainland, but the NHC will be keeping an eye on it.