Potential Tropical Cyclone Ten: Significant Impacts in the Carolinas Possible

Plenty of attention has been on Harvey this weekend making landfall as a major Category 4 hurricane near Rockport, Texas, and then causing catastrophic flooding in and near the Houston Metropolitan area. This will likely not change over the next several days, as Harvey continues to meander over South Texas, dumping waves of heavy rainfall. But another storm is beginning to take shape off the Southeast Coast. This storm has been classified by the National Hurricane Center as Potential Tropical Cyclone Ten, which was previously invest 92L that was followed since it was way out in the Atlantic. Wind shear and dry air over much of the Western and Central Atlantic had kept this system from organizing. However, this system has become better organized just off the South Carolina and Georgia coasts this afternoon.

A Tropical Storm Watch has been issued for much of the South and North Carolina coasts. The system may acquire enough tropical or sub-tropical characteristics for the National Hurricane Center to upgrade it to tropical or sub-tropical depression storm within the next 24 hours. If that happens, it will be named Irma. But this system will be more of a hybrid storm instead of purely tropical and warm core in structure. Strong winds far away from the center and deep convection may be lopsided to the east, as some southwesterly shear will remain over it. But this storm will cause some heavy rainfall, strong gusty winds and perhaps some coastal flooding and beach erosion during the hide tide cycles over the Eastern Carolinas and Southeast Virginia. Some of these impacts may also spread northward into Eastern Maryland and Delaware by Tuesday night. This will depend largely on how far north the storm tracks.

NHC 5-day Forecast on Tropical Cyclone Ten

NHC 5-day Forecast and Tropical Storm Watches for Tropical Cyclone Ten

At this time, we are expecting surface high pressure and a broad upper-level trough over Northeast to keep the storm heading more east-northeast after moving through the Carolina and Virginia coasts. As a result, the brunt of the storm will not impact areas further north. However, this storm may interact and partially phase with shortwave energy digging into the Ohio Valley. And when coupled with an upper-level jet streak over Mid-Atlantic coast, some forcing may expand well away from the center to allow light to moderate rain bands from the storm to move northward into parts of Eastern Pennsylvania, New Jersey, Southeast New York, and Southern New England region on Tuesday evening.

There are significant model differences on the interaction and northern extent of rain, as a sloppier phase between Irma resulting in a broad trough over the Ohio Valley, Northeast, and Western Atlantic would result in a much further east scenario with little to no rain at all. Additionally, if Irma becomes more purely tropical, it may have a tighter core of heavier rain, and thus no significant rain would expand to the Northeast Coast. But a dual-jet streak as shown by the GFS (linked above) is usually a signal for at least some precipitation. A further west scenario would also lead to a solidly heavy rain and wind event for the Southeast New England Coast.

Then this storm will likely head east-northeast further out into the Atlantic and become more extratropical in nature, as it completes the phase with the shortwave energy offshore. However, this storm will be generating large swells over the Western Atlantic, due to its enlarging wind field, as it goes undergoes more intensification from baroclinic processes. Thus, some rough surf and rip currents are likely as far north as the Southern New England coastal waters, regardless if any rainfall or winds of consequence reaches these regions. So if you have plans to be on the beach or shore over the next few days, take caution swimming or with small craft over the ocean.

Large swells along Mid-Atlantic and Southern New England coast from Potential Tropical Cyclone Ten by Wednesday

Large swells along Mid-Atlantic and Southern New England coast from Potential Tropical Cyclone Ten by Wednesday morning

Overall this storm is not likely to be extremely powerful and it should keep moving steadily, due faster flow along the East Coast. So we aren’t anticipating this storm to cause nearly as much as devastation and the catastrophic flooding that Harvey will produce over the next few days. But some significant impacts are likely in parts of the southern Mid-Atlantic region and preparations should be taken to protect life and property, especially along the Virginia and Carolina coasts, over the next few days. Stay tuned for updates on this Potential Cyclone Ten for any changes over the next few days. We will continue to monitor for trends on the model guidance and will pass any more new information on upgrades or warnings from the National Hurricane Center.