It's a simple message, and it comes from the heart: if you live in the southeastern United States, prepare a potential hit by Tropical Storm or even Hurricane Arthur later this week. Given the amount of tourists on Carolina beaches for the holiday weekend, it's probably the worst time of the year for a storm to threaten.

I covered the basic driving factors behind "possibArthur" this past Saturday, including:

  • the lack of a steering mechanism in the atmosphere, which will cause the storm to move slowly over the next five days;
  • warm sea surface temperatures, which are fuel for tropical cyclones;
  • winds are still marginally conducive to won't strengthen into a monster, but they'll allow possibArthur to turn into a tropical storm over the next few days.

The storm is becoming better organized both on satellite and radar imagery, and a hurricane hunter aircraft is currently investigating the system to see if the National Hurricane Center can upgrade the system to either Tropical Depression One or Tropical Storm Arthur in their 5 PM EDT advisory.

A tropical depression is a system that has winds less than 38 MPH; a tropical storm has winds between 39 and 73 MPH, and a hurricane has winds of or greater than 74 MPH.

The above spaghetti model plot — which plots multiple models' predicted path of the storm onto one chart, the result looking like spaghetti — shows that models generally agree that possibArthur will scrape the Carolina coast this weekend before heading northeast.

The uncertainty right now, provided the storm forms at all of course, is both how strong it will get how close it will remain to the East Coast beyond North Carolina. The GFS (global American) model brings it onshore early and keeps it relatively weak:

The ECMWF, the superior European model, strengthens it to right around minimum hurricane strength (75 MPH) and brings it into the Outer Banks of North Carolina before shooting it out to sea:

There are two other hurricane models that meteorologists can use to make their forecasts, called the GFDL and HWRF, and these both differ as well. The HWRF brings Arthur inland while the GFDL sends it skirting perilously close to the Outer Banks before moving out to sea.

The models generally agree that the system will become a tropical storm (winds between 39-73 MPH) today or tomorrow, while they disagree quite a bit on its peak strength. The system's winds are an issue that the National Hurricane Center will ultimately deal with once they release their first forecast tonight or tomorrow.

The storm's path and strength will also determine how much rain the I-95 corridor sees over the next week. The latest total rainfall forecast from the Weather Prediction Center shows more than an inch of rain for areas from Washington D.C. to Boston over the next several days, with totals going up or down depending on how closely the storm tracks to the coast.

Anyone who lives from Miami to Halifax has to watch this storm closely as one little change can drastically alter the system's future strength and path. Residents along the South and North Carolina coasts should be especially cautious and prepare for the potential for a prolonged strong winds, heavy rain, flooding, high waves, and a small storm surge. Start trimming trees and clearing out any debris, furniture, and decorations that could blow around in high winds.

If the hurricane hunter aircraft finds that the system has developed into a cyclone, the National Hurricane Center will release its first forecast at 5PM Eastern, followed by subsequent updates every three hours thereafter. Otherwise, their next outlook will be released at 8PM Eastern.

[Images via GOES, WeatherBELL, Gibson Ridge, and the WPC]