A low pressure system that exited the South Carolina coast on Saturday morning continues to drift south and slowly get better organized.  It is expected to develop into the season’s first tropical depression, and later, a tropical storm. Computer model forecast suggest the possible storm will take a turn to the north and may impact Mid-Atlantic coastal areas with high surf, wind and rain July 3 and 4.

If you’re considering heading to the Carolina or Delmarva beaches for Independence Day, you are strongly encouraged to monitor forecasts.

The disturbance has an 80 percent chance of becoming a tropical storm within 3 to 5 days says the National Hurricane Center. Assuming it does so, it would earn the name Arthur, and it would be the latest first named storm since 2004 (when Alex formed on July 31).

Tropical system dashboard

System type: Invest (Unclassified disturbance being monitored)
Location: 130 miles due east of Cape Canaveral, Fla.
Intensification potential: Medium (confidence: medium)
Landfall potential: Medium (confidence: medium)
Days from possible landfall: 3-5
Zones to watch for possible landfall: Carolina coast to Delmarva (confidence: medium)

Satellite image of the disturbance off the east coast of Florida at 8:40am.  The exposed low-level center is due east of Cape Canaveral, and all thunderstorm activity is displaced to the south. (NASA)

The disturbance is presently meandering to the southwest toward the Florida peninsula, but – thus far –  environmental conditions have not been working in its favor. There is currently minimal rainfall associated with it and it is very disorganized.  An aircraft reconnaissance mission is planned for later today to more closely investigate the central pressure and wind field. Its surface pressure has been falling over the past day.  (Impressively, global models – such as the European, GFS, and Canadian – have been forecasting this scenario as early as LAST Monday!)

Forecast tracks from various skillful models as of Monday morning. All agree on it lingering east of FL for a couple days before heading up the coast. Forecast tracks from various skillful models as of Monday morning. All agree on it lingering east of FL for a couple days before heading up the coast.

It is meandering in an area with virtually no steering flow, but that will change by Thursday when a significant trough (or cold front, currently centered over the central U.S.) picks it up and pushes it to the north and northeast… away from Florida and towards the Mid-Atlantic states.

So how strong could it get? One model forecast (ECMWF) actually brings the system up to borderline hurricane intensity right by the Outer Banks of North Carolina on Independence Day.  Another (HWRF) shows it making landfall in southern South Carolina on Thursday as a minimal hurricane.  It’s fine to be aware of the various model scenarios, but one should not read too much into the details of a particular forecast.

As with any weak tropical system, the primary threat is more likely to be rain than wind.  Most model forecast scenarios support a soggy stretch for the Mid-Atlantic coast coast July 3 and 4. A 7-day accumulated rainfall map is shown below, with fairly high values (2″+) from Florida up through New Jersey, along the coast. Note that some of the rain portrayed on this map for areas further inland is more related to the incoming cold front than the tropical system.

Seven-day rainfall forecast. (NOAA/WPC) Seven-day rainfall forecast. (NOAA/WPC)

In terms of when wind and rain are most likely to impact coastal areas, here are some initial thoughts, which may shift:

Carolina beaches: Thursday afternoon to Friday morning
Virginia beaches: Thursday night to Friday midday
Delaware and Maryland beaches: Friday

It is possible that wind and rain avoid or just skirt the Maryland and Delaware beaches, whereas the Carolina beaches are less likely to escape the brunt of this potential storm. While areas further inland – along and west of I-95 – should monitor the storm. direct effects from the storm aren’t particularly likely although it may draw some moisture into the front coming through Thursday.

Additional hazards – high surf, rip currents, and beach erosion – could impact coastal areas for a longer duration than wind and rain – spanning roughly Wednesday through Saturday.