Hurricane Isaias is pounding the Bahamas today with torrential rain and powerful winds as it passes through the Caribbean toward Florida’s East Coast. Isaias is expected to impact the Floridian coastline this weekend with a near-miss or landfall before making a possible second landfall in North Carolina on Monday.
Isaias is the ninth named storm of the 2020 hurricane season – the earliest “I” storm on record – but the first to pose a significant threat to large portions of the East Coast. As of 5pm Friday Isaias is a low-end Category 1 Hurricane with maximum sustained winds of 75 mph located over the southeastern Bahamas. The hurricane is drenching the Bahamas with torrential rainfall capable of producing dangerous flash-floods as it begins aiming for Florida on Saturday and Sunday. Leading outer bands could work there way into southeast Florida as soon as late Friday night.
The track of Isaias is uncertain but it will be steered by two primary mechanisms: an upper-level trough crossing into the Northeast Sunday and the Bermuda High over the Southwest Atlantic. Isaias will follow a weakness in the ridge produced by the incoming trough and squeeze between the two features, turning clockwise to the north upon nearing Florida then to the northeast towards North Carolina parallel to the Southeast Coast. With this general track in mind, there is wiggle room for Isaias to follow two more specific tracks each with their own sets of risks.
Scenario One: Florida Landfall
In the first track, Isaias would make landfall on Florida’s East Coast late Saturday or early Sunday. This would bring modest impacts to Florida but would prevent more substantial impacts elsewhere. Under this scenario, Tropical Storm and brief hurricane conditions would berate Florida for a time Saturday and Sunday, dumping 4-8″ of rain with local amounts to 12″ over Florida’s East Coast. The storm would then likely reemerge over the Atlantic where it would briefly re-intensify before making a second landfall between South Carolina and southern North Carolina as a tropical storm or borderline Category 1 Hurricane.
This first scenario would bring life-threatening flooding and storm surge to Florida’s I-95 corridor but would quell wind, rain, and storm surge to the Carolinas and pacify impacts in the Northeast. All impacts would not be avoided, however. A roughly 8-12 hour period of heavy rain should still be expected east of the Appalachians in the Northeast between Tuesday and early Wednesday.
Scenario Two: Florida Near-Miss, North Carolina Landfall
The second track would be a miss for Florida, instead resulting in a landfall over eastern North Carolina that would produce much more dangerous conditions there and in the Northeast compared to the first track. By avoiding landfall over Florida, Hurricane Isaias would gradually intensify off the Southeast Coast, swiping only coastal Florida this weekend with strong winds and heavy rain of 2-5″ before striking coastal North Carolina as a strong Category 1 or possibly weak Category 2 Hurricane.
Under the stronger second scenario, powerful storm surge, wind gusts as high as 90 mph, and heavy rains of 4-8″ could ravage the North Carolina coast. Isaias would then continue on as a Tropical Storm or borderline Category 1 Hurricane along the coast towards Long Island or Cape Cod before moving rapidly through the Northeast, still capable of producing life-threatening storm surge, wind gusts up to 70 mph, and 3-6″ of rain in a time span of just 6-10 hours. The bulk of the rain would fall near the coast but some heavier rain could also develop over eastern New York and northern New England, especially if Isaias phases with the aforementioned trough and undergoes “extra tropical transition,” by which it will gain features of both a tropical cyclone and a Nor’Easter.
Factors Determining Track
The factors controlling which track to take are fairly unpredictable. Isaias is currently combating a region of wind shear – change in wind speed and direction with height – as of Friday afternoon. Wind shear disrupts the circulation of tropical cyclones and there is already evidence of that occurring. If Isaias is weaker when approaching Florida, it will be slower to curve to the northwest and then to the northeast, favoring track 1. If Isaias is stronger, it will make a faster turn, favoring track 2.
Despite the wind shear, Isaias is standing strong, as intense deep convection builds symmetrically about its center as demonstrated on visible and infrared satellite.
Further supporting Isaias’s strength are measurements of central pressure taken by reconnaissance aircraft that show a decrease in minimum of central pressure of 991 mb at 2pm ET compared to 992 mb at 11am ET. So despite the wind shear and lack of organized eye-wall, Isaias is holding up strong. This gives more credence to storm track 2.
Ultimately, the differences in factors that lead to Isaias making its first landfall over Florida versus North Carolina are subtle. The most optimal forecast track is a blend of the two, featuring a “near miss” of Florida’s East Coast such that Isaias makes landfall over North Carolina southwest of the Outer Banks, allowing for some weakening over eastern North Carolina before approaching the Northeast as a tropical storm. However, a more direct landfall into Florida’s east coast; which would spare the Carolinas and Northeast; or a land-fall over the Outer Banks; which would lead to significant impacts in North Carolina and the Northeast; are both possible.