Monitoring late week coastal low off the southeast US

Coastal low later this week may acquire tropical characteristics as it moves toward the Carolinas for the weekend

A coastal low forecast to develop north of the Bahamas by Thursday into Friday may try to take on some tropical characteristics as it brings gusty winds, rough seas and the possibility of coastal flooding from northeast Florida through the Carolinas by the weekend.

The question is less whether the coastal low develops but rather if it can transition from a decidedly non-tropical frontal low to one that resembles an independent tropical system. In order to do so, it would need to generate persistent thunderstorm activity near the low-pressure center to warm its core.

Cyclone phase space diagram for the coastal low we’re tracking for late week. Letter “A” denotes the low-pressure position late Thursday and “Z” the low-pressure position on Monday over the Mid-Atlantic. The structure most closely resembles a tropical cyclone when the phase space lies in the warmer colors (reds and magentas). Models suggest the system could acquire borderline tropical features (shallow warm core) on Friday and Saturday as the low-pressure moves over warm Gulf Stream waters. Credit: Dr. Robert Hart/Florida State University

The system’s proximity to the nearby Gulf Stream – the ribbon of warm water that parallels the southeast coast – may be the boost it needs to briefly turn subtropical this weekend.

The distinction between a non-tropical and subtropical area of low-pressure is somewhat pedantic in this instance as regardless, the system will bring gusty winds, rough seas – including the risk of life-threatening rip currents – and the potential for coastal flooding from Florida’s First Coast by late week into the Carolinas for the weekend. If the system does acquire tropical characteristics, there is the possibility for some additional strengthening so these coastal areas should continue to monitor its progress.

The coastal low is not expected to adversely affect our weather here in southeast Florida, although cold temperatures aloft associated with an attendant upper-level cutoff low could enhance the risk for severe weather across South Florida by Thursday or early Friday.

Hurricane Nigel large and largely unchanged

Hurricane Nigel continues to defy forecasts for strengthening, which had initially called for a major (Category 3) hurricane by today. The still-Category 1 hurricane scraped out a large, nearly 90-mile wide eye over the past 24 hours (a typical hurricane eye is closer to 30-40 miles across) and hasn’t yet been able to leverage environmental conditions largely conducive to strengthening. The large size of the hurricane may be a contributing factor to its arrested development, as larger hurricanes are less prone to intensity fluctuations in both directions.

Nigel has another 12-24 hours to strengthen before it makes a sharp turn into the North Atlantic graveyard late tomorrow into Thursday. The hurricane is no threat to land.

Next disturbance set to roll off Africa by tomorrow

Another tropical wave is poised to leave the coast of Africa by later today into tomorrow. Models were initially bullish on its development prospects but have softened some in recent runs. Regardless, development still looks more likely than not into the weekend as the system moves generally west-northwestward. For now, it’s no concern for us stateside.

About the Author:

Michael Lowry is Local 10's Hurricane Specialist and Storm Surge Expert.