It’s been a wet and breezy day here in Reston, with rains increasing recently; Flash Flood Warnings have been posted for much of the area (though Reston is left out of the polygon for now). Haven’t had any issues with power disruptions or any other weather-related issues thus far.

Rains have been generally moderate and steady; Irene’s interaction with the trough seems to have affected banding pretty considerably. Rains have recently picked up here and this rainfall rate may be here to stay. I suspect additional Flash Flood Warnings will be raised further west as time goes on.

I’m on the second floor of a very sturdy structure that seems resistant to power interruption (have only lost power once in 4+ months of living here) so I am confident that we’ll be fine. Will periodically update as Irene gets closer; its center is about to emerge back into the Atlantic, which should help it maintain Category 1 hurricane strength through landfall on Long Island.

NHC’s 5PM track and wind field forecast (above; click to enlarge) indicates that the strongest tropical storm-force winds will impact the Charleston area northward around sundown tomorrow. As a result, a Tropical Storm Warning has been posted for Charleston and Berkeley counties (Dorchester County may see some gusty winds but it looks as if the bulk of the wind will remain to the northeast).

Wind forecast

NWS Charleston is forecasting 25-35 MPH sustained winds with gusts to 45 MPH over much of the area Friday into Friday night; from IOP northward along the coast, the wind speed forecast increases to 35-45 MPH sustained winds with gusts to 55 MPH. (For reference, the minimum wind speed criteria for a severe thunderstorm warning is 58 MPH.)

Storm surge

Storm surge is not expected to be a factor. Unfortunately, Irene’s arrival coincides with a period of enhanced astronomical high tides, which combined with already high surf and rainfall may help to flood downtown Charleston.

Rainfall forecast

The latest 2-day QPF chart indicates the most tremendous rains will remain well offshore; however, an inch or two of rain (at a minimum) is really not out of the question from Irene.

What to watch

Now’s the time to pay less attention to models and more attention to what the storm is actually doing. Irene is forecast to finish turning north tonight; that will be critical to the forecast for Charleston. The other side is to watch for wobbles as well; a jump in track to the left could make a big difference in actual impacts. Finish your preparations tonight; winds like this can still knock out power for a few hours (especially in areas with overhead lines) so it’s good to be ready.

Irene is a picturesque and dangerous Category 3 storm with winds at least at 115 MPH; Dr. Rick Knabb, hurricane expert at The Weather Channel, suspects it may be stronger. The forecast track makes this less of a South Carolina event and more of an Outer Banks/Mid-Atlantic/New England event, which will impact millions upon millions of people who don’t normally see this kind of activity. Right now, the extended track puts landfall just east of Boston Sunday evening/early Monday morning; again, 4-5 day forecasts have significant margins of error in both intensity, timing, and location.

As crazy as this sounds, Irene may have more impacts on me in Reston, VA than it will in Charleston, SC.

Specifics are still up in the air some with regards to impacts in the Lowcountry. NHC is outlining a 30% chance of tropical storm-force winds along the Charleston County coast within 120 hours; this probability increases to 40% along the Grand Strand. Tropical storm-force winds are 39 MPH and greater; for reference, the National Weather Service criteria for severe thunderstorm wind is 58 MPH. I suspect we will get pretty clear guidance from the NWS office in Charleston later this evening or first thing tomorrow surrounding specific impacts, and I will update here when those statements start to roll in.

There will be a new track shortly, but it does appear that tropical storm force winds will be a factor from the Charleston County coast north on Friday night, assuming Irene follows the forecast path perfectly. Any wobble in the track could have drastic impacts on the forecast.

And the Boston landfall as a hurricane is just blowing my mind…

Source: U.S. Naval Research Laboratory

The 5am track superimposed on the models indicates that the 11am track very well may move again. This is great for South Carolina; this is not so great for the Outer Banks of North Carolina.

New track in 40 minutes; will update then.

00z GFS at 96 hours keeps the center of Irene well offshore.

I’m cautiously optimistic that this 00z GFS, initialized with lots of quality upper-air data, may pan out. Time will tell — and we have so much time for so much to change — but the rightward trend today is promising for keeping Irene’s center off the SC coast.

This GFS run is not so good for the Outer Banks. Morehead City really takes it on the chin in this run.

This is just one model run of many — though it is well-mixed with the consensus, there’s too much room for error still. Stay tuned…

San Juan radar depicting Irene's eyewall.

Hurricane Irene deepened pretty significantly this evening, intensifying to a Category 2 storm with winds of over 100 MPH as found by a Hurricane Hunter plane. NHC issued a special advisory at 8:30 to upgrade the intensity forecast; Irene should now be a major hurricane by tomorrow afternoon (if not sooner). The Bahamas are going to take a beating from this, it looks like.

The forecast path, originally bulls-eyeing Charleston this morning, shifted north at 5PM to put the center onto Horry County. This follows a majority of the model guidance nicely (including the Euro, darling of the NHC this season). 00z model runs should be infused with a lot of good upper-air data from dropsonde missions as well as special RAOBs released by many East Coast NWS offices so those models will really be telling; they’ll be out around midnight or so.

It’s still far too early to say for sure what will happen, but I think it is a safe bet at this point that weather conditions will begin to deteriorate along the SC coast Friday and be at their worst Saturday. Probabilities of at least tropical storm-force winds along the coast are steadily increasing, so continue to monitor the NHC forecasts.

More in the morning when the new models have had a couple runs…

Animation demonstrating track of Irene and how it has evolved. Click it to start.

As the animation above shows, if you’re in the centerline of Irene’s track, wait six hours and you’ll likely be out of it. The models have persistently wanted to go further right; they may be getting a better handle on a bit of energy that may strengthen the trough which will help deflect the storm further away. Will watch the models carefully. So far, NHC has erred on the left side of the guidance envelope. More good news: The GFS, which has pegged Irene for Charleston pretty consistently over the last couple days, is trending rightward and now just grazes the SC coast.

I have to reiterate: It’s not time to panic; it’s time to prepare.

Interesting shift in the 12z run of the early-cycle models (completed a little more than one hour ago), bringing the consensus even further eastward closer to the Grand Strand. The NGPI model even goes as far as to recurve it out into the Atlantic, but given the strength of the ridge I’m not sure about that just yet…

Source: NCAR Tropical Cyclone Guidance Project