Irene could strengthen to dangerous category 4

After weakening slightly overnight, Irene’s strength has come back with winds currently measured at 115 mph. (NOAA) ( NOAA Environmental Visualization Laboratory )

Swirling through the southeast Bahamas, Hurricane Irene has intensified this morning, reaching major category 3 status, with peak sustained winds of 115 mph. Hurricane warnings continue for all of the Bahamas where 6-12 inches of rain are expected in addition to punishing, hurricane force winds. A potentially devastating storm surge of 7-11 feet is possible in areas with onshore winds near the center of Irene.

NOAA track forecast

Irrespective of whether the storm makes a direct hit at particular coastal locations from North Carolina to New England, significant impacts are quite possible including torrential rain, coastal flooding and damaging winds.

Irene’s current presentation

Irene exhibits an unmistakably visible eye surrounded by very tall thunderstorms on satellite imagery. Ingestion of dry air and some wind shear probably adversely affected Irene’s health last night and may be to some degree right now, but strengthening has resumed. Further intensification is expected as it continues to move over 85+F water and effectively fends off the environmental resistance. The storm may well reach category 4 levels with peak winds near 135 mph in the next couple days according to the National Hurricane Center (NHC).

Track forecast

The vast majority of the model forecasts for Irene have shifted eastward quite drastically in recent days.

South of North Carolina

It is no longer likely Irene will make landfall south of the Outer Banks of North Carolina. This should give breezy and hot weather for Florida, Georgia, and South Carolina as the week draws to a close. With an outside chance for a tropical-storm strength wind gust in a rain shower along the immediate shoreline anywhere south of say, Myrtle Beach, SC, I would expect folks along this part of the U.S. Atlantic Coast to see a canopy of cirrus outriders from Irene overhead or just off to their east. The ocean will be rough, no doubt, with rip currents a serious risk. But the dangerous part of Irene will very likely remain way offshore … 100-200 miles at least.

North Carolina to the Jersey Shore

As Irene moves poleward from there over the weekend, from the latitudes of the North Carolina coast to those of the Jersey Shore, the spread in the track guidance increases and the forecast obviously gets more difficult.

The greater uncertainty at these lead times makes outlining potential impacts a complicated and potentially misleading exercise. One can not forget that the average four-day track error is on the scale of the storm itself. And this is not even accounting for the intensity errors and size miscalculations that also play a critical role in determining who gets what kind of weather.

But still, the collection of possible tracks offered by both the global weather-prediction systems and the specific hurricane models are sending a message. And that is the core of Irene, in whatever health it’s in by the time it reaches those relatively northern locales, may graze the eastern tip of the Outer Banks on Saturday evening at its closest Mid-Atlantic approach. For the record, the NHC official forecast projects an intensity of roughly 125 mph as it nears the Outer Banks Saturday evening,

Though the National Weather Service (NWS) is appropriately and rightfully vague in the weekend forecast for these places, there are some general aspects of the sensible weather that we can take a stab at.

The large radius (205 miles) of tropical storm force winds (sustained 39-73 mph) expected with the storm on its western side even at those northern latitudes suggests locations along the immediate coast could still experience legitimate tropical storm conditions with high seas, coastal flooding and heavy rain beginning Saturday in North Carolina and Virginia and lasting through the weekend further north toward the Delmarva Peninsula and New Jersey. If the core remains intact, then the Outer Banks could, repeat could, get into the low-end hurricane conditions. Remember the worst impacts are usually east and northeast of the center.

Again, there is lots of speculation here, because the worst of Irene could easily stay offshore as suggested by the majority of the guidance.

New England

Taking the forecast another step forward, there is a chance that Irene will make landfall in southern New England in about five days (but remember too that five days ago some expected Irene to hit south Florida!). Cooler ocean waters in the 70s and stronger, drier, winds aloft could very well do significant damage to Irene prior to a landfall and allow it to arrive in ill-health. Of course there’s a long way to go before specifics can be nailed down, but residents along coastal New York and southern New England should keep an eye(rene) on Irene. It has the potential to be a dangerous storm in that region. Flooding rain, a coastal surge, and damaging winds are still a possibility, especially for any areas on the east side of the storm if the center moves over the land.

Limits of predictability

Looking into forecasts this far out brings me to one last point. Some might say that this entire situation with Irene is setting up to be another false alarm for the Southeast Coast (south of North Carolina).

Evolution of Irene’s track forecasts from National Hurricane Center

I would argue instead that alarm bells should have never been rung in the first place. There has not yet been, nor is there now, enough certainty in the forecast to skillfully predict where Irene will make landfall (if it does at all).

NWS forecasters are well aware of this, as are the experts at NHC. That is exactly why they have used extreme caution in their tone and have been appropriately hesitant to express confidence about a forecast that still carries huge error bars while life and death are potentially at stake. Ultimately, they are the ones with the accountability. The science can only take us so far, and to expect more than that right now is unreasonable and potentially unwise.

Capital Weather Gang Hurricane Tracking Center