August 3, 2020

Hurricane Isaias Makes Landfall In N.C., Strong Winds Likely Up I-95 Next Two Days


After several days of changing its appearance more than a theater star—yet maintaining its intensity against the odds—Isaias made landfall at 11:10 PM EDT near Ocean Isle Beach, North Carolina with 85 MPH winds. The system will push into eastern North Carolina overnight into Tuesday as it picks up speed and races up the Interstate 95 corridor. Widespread power outages and flash flooding are possible along the path of the storm as it heads toward Maine.

Show someone a satellite image of the hurricane making landfall in North Carolina and almost no one would guess that this thing has a solid core producing sustained winds of 85 MPH:


This has been quite the storm to follow over the last week. Hurricane Isaias organized its inner core and began to strengthen just as the eyewall began scraping the South Carolina coast. It seems counterintuitive, but we're pretty fortunate that strengthening happened now as opposed to a couple of hours ago; the hurricane could've strengthened more if it had more room to gobble up instability over the open water. A team of Hurricane Hunters found 85 MPH winds on the eastern side of the eye (with flight-level winds of  100+ MPH!), which isn't great news for coastal North Carolina, which will experience those hurricane force winds for several hours tonight.

As I explained in last night's post, the system will begin drawing some of its energy from the jet stream as it accelerates northward up the East Coast. This process is known as extratropical transition, resulting in a system that'll more closely resemble a strong nor'easter than a hurricane by the time it reaches New England on Tuesday night. This transition will allow Isaias to grow in size, exposing a larger area to strong winds and heavy rain.

Forecast


Isaias will make 'official' landfall—the center of the eye crossing the coastline—near Shalotte, North Carolina, around midnight, with sustained winds of about 85 MPH. The National Hurricane Center's forecast shows Isaias following a straight shot up the coast, reaching the Delmarva by Tuesday morning, New York City by Tuesday evening, and moving through Maine into the Canadian Maritimes on Wednesday.

Hurricane warnings are in effect for the counties where the storm is making landfall. Tropical storm warnings are in effect for the entire coast from Charleston, South Carolina, through southern Maine, including many inland areas where folks wouldn't necessarily expect to witness tropical storm conditions. Anyone in the tropical storm warning can expect a period of sustained winds of 35+ MPH, as well as the potential for flash flooding from heavy rain.

Wind & Storm Surge


The hurricane isn't going to wind down immediately once it comes ashore. The momentum of the storm and the influence of the jet stream will allow it to gradually lose strength, exposing lots of densely populated communities to a period of strong winds and even higher gusts.

Widespread power outages are likely from the point of landfall and northward through the New York City metro area, with scattered power outages possible elsewhere. For what it's worth, the NHC's evening forecast shows Isaias making it to New York City with sustained winds of 65 MPH with higher gusts. You can only hope folks in this region appreciate how strong the winds will be and how much damage those winds can do to the trees and power lines in these areas.

Storm surge is an issue since the storm will track so close to the coast. Onshore winds will push a surge of seawater into coastal communities. It won't be a big surge—a few feet deep in the hardest-hit communities—but even a few feet is dangerous if it swamps an occupied vehicle or it swamps a one-floor house or a condo complex. The NHC's map of potential storm surges is above.

Rain


Flash flooding is likely across areas in Isaias' path over the next couple of days. The Weather Prediction Center shows 3 to 5 inches of rain falling along and to the west of the center of the storm, which includes communities along and west of Interstate 95. The greatest rainfall totals are possible on the eastern side of the D.C. and Baltimore metro areas during the day on Tuesday.

Tornadoes

Tornadoes are an ongoing threat as the storm moves ashore. Tornado watches are in effect for almost all of eastern North Carolina tonight as Isaias makes landfall, and the threat will follow the eastern part of the storm as it moves up the coast. Multiple tornadoes have already occurred around Wilmington, and the supercells that produced them are hauling tail at highway speeds.

Here's the SPC's severe thunderstorm outlook for the rest of the night through 7:00 AM EDT on Tuesday...


...and here's their severe thunderstorm outlook for the day Tuesday and into early Wednesday morning:


Tropical tornadoes happen quickly and that speed reduces tornado warning lead time. Stay alert and make sure you've got a way to receive warnings the instant they're issued. Modern smartphones are equipped with emergency alerts that can be activated through the notifications section of your phone's settings.

[Radar: Gibson Ridge | Satellite: NOAA]

You can follow me on Twitter or send me an email.

Please consider subscribing to my Patreon. Your support helps me write engaging, hype-free weather coverage—no fretting over ad revenue, no chasing viral clicks. Just the weather.
 

August 2, 2020

Isaias Flirts With Hurricane Strength; Monday Night Landfall In Carolinas Likely


Tropical Storm Isaias keeps fighting back against the atmospheric forces trying to tear it apart, managing to maintain its strength on Sunday as it paralleled Florida's east coast. Forecasters expect the storm to flirt with hurricane strength as it accelerates toward landfall in the Carolinas overnight Monday and into Tuesday. Isaias has the potential to be a disruptive storm as it traverses the U.S. East Coast and brings dangerous wind gusts and flooding rain to densely populated areas.

The track forecast for Tropical Storm Isaias hasn't changed much in the last few days. That kind of consistency is a good thing since it's given folks in harm's way ample opportunity to prepare for the potential for gusty winds, heavy rain, and power outages. The latest forecast from the National Hurricane Center shows the storm picking up speed over the next 24 hours as it approaches the Carolinas. Landfall is likely on Monday night around Myrtle Beach, S.C., or Wilmington, N.C.


Accordingly, tropical storm watches and warnings are in effect for a large swath from central Florida to southern Connecticut. A hurricane watch is in effect from South Santee River, S.C., to Surf City, N.C., just in case Isaias strengthens back into a hurricane. The map above shows all the county-based alerts in effect as of 11:00 PM on Sunday. The difference between a 70 MPH tropical storm and a 75 MPH hurricane is negligible, so the folks near the point of landfall can expect a period of damaging winds regardless of whether Isaias makes it back over that threshold or not.
Source: NOAA

Tropical Storm Isaias looks pretty healthy tonight. It's got strong thunderstorm activity bubbling near the center of circulation. There's intense transverse banding in the outflow on the northern edge of the storm; this scalloped ridging is the result of turbulence and it's common around healthy storms with robust convection that's venting lots of air into the upper atmosphere.

Isaias is going to start losing some of its pure tropical-ness pretty soon. So far, the storm's been influenced by two major features around it: a strong Bermuda High to its east that's kept it from running back out to sea, and an upper-level trough over the Mississippi Valley that's kept it from heading west into the Gulf. These two features combined are responsible for its very careful curve from the Caribbean into the Carolinas. 

Isaias has been lopsided ever since it crossed Andros Island in The Bahamas. That's why it was mostly just breezy and showery on Florida's East Coast on Sunday even though the center of the storm is so close to shore that a daredevil could intercept it with a kayak.
Source: Tropical Tidbits

However, the tropical storm is going to start to 'feel' that upper-level trough come Monday, deriving some of its energy and influence from the jet stream like a Nor'easter would. This will allow the storm to grow in size and accelerate up the coast.

Once it begins to grow and its structure changes a bit, the heavy rain and winds will start wrapping around and filling in the western side of the storm. This is why the forecast looks so much rougher in Wilmington than things look in Cape Canaveral right now, even though the center of the tropical storm is just a few dozen miles offshore of NASA's launch pads.

Wind & Storm Surge

Source: NHC

The strongest winds and heaviest rains will follow the core of Isaias as it moves inland on Monday night and Tuesday. Myrtle Beach and Wilmington will take the brunt of the storm; these areas could see a period of hurricane force winds and more than half a foot of rain. Widespread power outages are likely in areas that see strong winds. Keep your cell phones charged and your flashlights close by on Monday night.

Strong winds will continue into the Mid-Atlantic and Northeast on Tuesday and Wednesday. Tropical storm conditions (sustained winds of 40+ MPH) are possible as far west as Washington D.C. and Philadelphia. The latest NHC forecast calls for the storm to have maximum sustained winds of 45 MPH when it moves over New York City on Tuesday evening. 

Even a strong tropical storm can lead to a storm surge along the coast, especially where the storm makes landfall. A storm surge of 2 to 4 feet above normal tide levels is possible between Edisto Beach, S.C., and Cape Fear, N.C. That doesn't sound like much, but it's life-threatening for homes along the coast that are susceptible to storm surge flooding, made even worse by the fact that rescue crews may not be able to reach homes inundated by flooding until after the worst of the storm has receded.

Heavy Rain & Flash Flooding


Flash flooding is likely along the Isaias' track as it moves up the coast. The heaviest rain is likely in the Carolinas and Mid-Atlantic; the Weather Prediction Center calls for widespread totals of 3-5 inches from the point of landfall through New England, with higher totals likely in some locations if they get caught under a particularly heavy band.

Flooding from heavy rain is the leading cause of death in a landfalling tropical cyclone. It only takes a few inches of moving water to lift a vehicle and carry it downstream. It's impossible to judge how deep the water is until it's too late, and sometimes the road is even washed away under the moving floodwater.

Tornadoes


Tornadoes are always a threat when a tropical cyclone makes landfall. There's enough low-level wind shear in these systems to spawn quick tornadoes, especially along and to the east of the storm's forward motion. Right now, the greatest threat for tornadoes exists across eastern North Carolina on Monday night and Tuesday, where the Storm Prediction Center has issued a slight risk for severe weather.

Tropical tornadoes sometimes occur so quickly that the normal tornado warning lead time is reduced to just a few minutes at most. Stay close to safe shelter if you're near the path of the storm, and make sure the emergency alerts are activated on your smartphone. (The option is usually under the settings for notifications.)


You can follow me on Twitter or send me an email.

Please consider subscribing to my Patreon. Your support helps me write engaging, hype-free weather coverage—no fretting over ad revenue, no chasing viral clicks. Just the weather.
 

August 1, 2020

Hurricane Warnings Continue For Florida As Struggling Isaias Approaches Land


Hurricane warnings remain in effect for much of eastern Florida this afternoon as Tropical Storm Isaias begins to move away from The Bahamas. The storm is struggling against a stream of dry air and wind shear trying to tear its convection apart, but it wouldn't take much reorganization to regain some of its strength. Florida will begin feeling the effects of the storm tonight into Monday before the system accelerates up the East Coast through the middle of the week.


Isaias is a resilient storm. The storm lost some of its strength and organization on Saturday as dry air and wind shear chomped away at its structure. The "eye" of the storm was fully exposed at one point, shown above, looking more like a swirl of shampoo in a draining bathtub than an ominous hurricane.

It's tried to get its act together since then. As of about 7:00 PM EDT, strong thunderstorms are trying to redevelop on the northern side of the circulation, and it wouldn't take much organization to allow the storm to regain its footing. Satellite data and aircraft reconnaissance showed the storm teetering between 70 and 75 MPH late this afternoon, which is the line between tropical storm and hurricane. There's not much of a practical difference between a strong tropical storm and a minimal hurricane. Given the uncertainty and the storm's tenacity, tropical storm and hurricane conditions still appear likely over a large swath of the Florida Peninsula over the next 24-36 hours.

The 5:00 PM forecast from the National Hurricane Center calls for Isaias to regain hurricane strength as it comes perilously close to landfall in Florida. The storm will scrape Florida's east coast through Sunday evening before it moves back over open water toward the Carolinas. Watches and warnings will accompany the storm up the coast; remember that these advisories don't only exist along the shoreline, and hurricane and tropical storm force winds are possible well inland from the coast.


Heavy rain will remain the greatest threat from Isaias the farther north you go. The Weather Prediction Center's rainfall forecast this afternoon paints 3-5 inches of rain along the path of the storm, which covers almost the entire length of Interstate 95. This much rain falling this fast will lead to the potential for widespread flash flooding, especially in areas that have seen heavy thunderstorms recently.

[Satellite: NOAA]

You can follow me on Twitter or send me an email.

Please consider subscribing to my Patreon. Your support helps me write engaging, hype-free weather coverage—no fretting over ad revenue, no chasing viral clicks. Just the weather.