TD 3 to Brush Florida’s East Coast

A tropical disturbance over The Bahamas gained enough organization on Monday for the National Hurricane Center to christen it Tropical Depression 3. Although this depression is headed toward the U.S., it will likely carve out a path that keeps it just off the Southeast coast, bringing little more than gusty winds and a few strong showers and thunderstorms.

As of 5 pm EDT, TD 3 was centered about 120 miles southeast of Palm Beach. The depression was tracking northwest at 13 mph across the warm waters between the Bahamas and South Florida, where sea surface temperatures were around 30°C (86°F). Visible satellite images and scatterometer data showed a closed circulation northwest of Andros Island, but not an especially strong one; sustained winds were just 30 mph.

Figure 1. Visible-wavelength satellite image of TD 3 at 2015Z (4:15 pm EDT) Monday, July 22, 2019. Dry air on the west side of TD 3 was feeding into the system's thunderstorms, creating strong downdrafts evidenced by long surface-based lines of cumulus clouds moving westward toward the east coast of Florida. Storms that are struggling with dry air commonly exhibit this feature, and you can bet TD 3 will be slow to strengthen because of the dry air. Image credit: tropicaltidbits.com.

Originally tracked as Invest 94L, this disturbance fought long odds. As recently as Sunday night, the chance of development was pegged by NHC as just 10%. TD 3 beat the odds by generating just enough showers and thunderstorms (convection) on Monday to fend off the effects of light to moderate wind shear and surrounding dry air.

A broad arc of convection wrapped around the north and east sides of TD 3 on Monday afternoon. Cloud tops were warming by late afternoon, though, a sign that the convection was weakening. Thunderstorms could reintensify on Monday night around TD 3 in tandem with the typical nighttime peak of tropical convection.

Figure 2. WU depiction of official NHC forecast track of Tropical Depression 3 as of 5 pm EDT Monday, July 22, 2019.

Outlook for TD 3: a U.S. sideswipe

TD 3 is already in the midst of a classic recurvature, as its northwest track will arc toward the north and northeast over the next couple of days. This track will largely parallel the Southeast U.S. coast, putting coastal areas mainly on the weaker left-hand side of the system. TD 3’s closest approaches to land will most likely be early Tuesday, when it passes near Palm Beach, and early Wednesday, when TD 3 or its remnants move over or near the North Carolina coast, finally sweeping out to sea from the Outer Banks.

NHC predicts that TD 3 will remain a depression until it becomes entangled with a frontal zone and loses its identity on Wednesday, somewhere in the vicinity of the North Carolina coast. Wind shear will remain light to moderate through Tuesday (5 – 10 knots), and TD 3 will be passing over a region of high oceanic heat content, so if this depression can keep dry air at bay, it might briefly become a minimal tropical storm, in which case it would be named Chantal.

Whether or not it earns a name, TD 3's main impact is expected to be squalls that dump several inches of rain across eastern Florida and The Bahamas. Rainfall of up to 3” may extend further north along and near the coast as far north as the Outer Banks by Wednesday, by which point increased wind shear will hasten the transition of TD 3 into a wave along the midlatitude front.

Dr. Jeff Masters contributed to this post.