Lookout for Frontal Remains: Tropical Storms May Form

Locally the heat and humidity continue until Wednesday at the earliest. Heat advisories may be needed soon. Main story discusses why cold fronts can create tropical storms, and if we need to watch for one soon.

NWS Charleston Forecast Max Heat Index (Tuesday)
NWS Charleston Forecast Max Heat Index (Tuesday)

FRONTAL TROPICAL STORMS:

While the majority of tropical storms in the Atlantic Ocean form from African waves, some tropical storms spin up off the decaying remains of cold fronts. In certain patterns, a cold front is able to pass across the eastern US and make it to the Gulf of Mexico or the Western Atlantic. When this occurs during a period of warmer water temperatures, there is an increased threat of tropical storm genesis. If warm water is in place, all a tropical storm needs to get started is moisture and vorticity in the atmosphere. The remains of cold fronts bring a plume of moisture that is needed, as well as pockets of low level vorticity.

Since there is often high shear, competing vorticity, and a large expanse of dry air alongside the front, tropical storms that form this way remain weak until they move away from the frontal zone (if they ever do). Since cold fronts in our region move west to east, tropical storms that form off a front in the Western Atlantic are often no threat to our region (or land at all). However, a tropical storm that forms this way over the Gulf of Mexico will almost always make landfall in the United States. These storms can be a "backdoor" threat to the Low Country when they track over the Florida Panhandle and into GA/SC.

This situation has happened before and could happen again next week. A few weather models are indicating a broad area of vorticity forming in the stalled remains of Wednesday's cold front (Over the NE GOM). While model support is weak (and weakening), I will be watching the area over the Gulf for a potential threat. IF a tropical storm were to form it would most likely remain weak, be short lived, and bring an increased chance of rainfall Sunday-Tuesday. Currently the only model support is from the EPS and a few GEFS members.

LOCAL WEATHER:

The morning starts off with a weaker Atlantic ridge off of the Low Country, and a surface trough over the inland SE. Further west, a large ridge remains centered over the Southern Plains. This feature will continue to bring a stifling heat wave to Texas, Oklahoma, the Deep South, and the Gulf Coast. The ridge just manages to cover the Low Country, so the day will feature a NW flow. Surface winds will be very light, but just out of the south and south west. Cloud cover will remain low for most of the day as there is low vorticity and dry air at the surface and 750mb. Precipitation will be limited by the same factors, but weak boundaries like the seabreeze will form some isolated showers. These showers have the potential to bring high precipitation rates as PWATs are around 2". Most areas will likely not receive rainfall until Wednesday.

High temperatures will be in 90s across the Low Country. Lower 90s along the coast and over the lakes, mid 90s along the 17 corridor and northern Low Country, and upper 90s across the southern Low Country. Heat index values will be higher than Monday, and closer to what we saw over the weekend. Highest heat indexes will be around 107-109 in the alt 17 corridor.

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