August 29, 2023

Destructive winds, widespread flooding likely far inland as Hurricane Idalia makes landfall

Hurricane Idalia is picking up speed toward northern Florida on Tuesday night as the storm continues to grow in strength and size over the sultry waters of the eastern Gulf of Mexico.

This is a deadly serious threat for coastal communities in the path of the storm, many of which have not witnessed a storm this powerful in the region's living memory.

While the coastline faces the life-threatening prospect of 10+ feet of storm surge and the full force of a major hurricane, this storm's impacts will extend far inland. This is not just a coastal threat, and these far-reaching storms often catch folks off-guard when they're hundreds of miles from the point of landfall. That's what I'll focus on here.

The storm's destructive winds, widespread flooding, and tornadoes will extend far inland from the point of landfall, exposing a large swath of northern Florida and coastal sections of Georgia and the Carolinas to significant and potentially long-lasting impacts from this powerful storm.

Hurricane Idalia spent Tuesday taking advantage of a favorable environment to rapidly intensify as it heads toward the western coast of Florida. The storm's maximum sustained winds crossed 100 mph on Tuesday afternoon, with the National Hurricane Center (NHC) expecting the Idalia to make landfall early Wednesday morning as a major hurricane.

The storm is likely to intensify all the way up to landfall, which could mean its maximum winds could climb to 120 mph or higher by the time the eyewall crosses the marshy coastline of Florida's Big Bend, likely near the community of Cedar Key.

Conditions will go downhill in a hurry as Tuesday night settles in, and the hurricane's high winds and drenching rain will quickly push ashore through the overnight hours as the storm makes landfall early Wednesday morning.

High winds and power outages

Idalia's ferocious winds, increasing speed, and the marshy terrain in the hurricane's path will allow the storm to maintain its intensity as it pushes inland through the day Wednesday.

Destructive winds are likely across much of northern Florida and southern Georgia, where hurricane warnings are in effect from Tampa to Tallahassee and north past Valdosta. Tropical storm warnings extend even farther inland, covering most of northern Florida—including Orlando and Jacksonville—as well as southeastern Georgia and all of coastal South Carolina.

Winds of 120+ mph will push into Florida's Apalachee Bay, which has seen exactly zero major hurricanes in recorded history. NWS Tallahassee is stressing that this is an unprecedented event for the region, and it's likely going to be the strongest hurricane to affect Tallahassee proper in living memory.

Given the marshy terrain and swift forward motion, it'll take a while for Idalia to lose steam. Sustained winds of 75+ mph are likely well into southern Georgia during the day Wednesday. Sustained winds of 60 mph will likely follow the storm all the way to Charleston, South Carolina, by the overnight hours Wednesday into Thursday.

Such a widespread wind event will lead to a significant blowdown of the dense forests that cover this portion of the southeastern United States. Expect many impassable roads for days after the storm, especially smaller and less-travelled roads. 

Source: NWS

Hundreds of thousands of homes and businesses will remain without power for many days after the storm, with the worst-hit areas likely going without electricity for several weeks as crews quite literally rebuild the power grid.

These widespread power outages will be a major disruption for folks who live in the region.

Communities that experience prolonged blackouts will see their perishable foods spoil and few options to buy groceries or other necessary supplies. Cooking will be extremely difficult without natural gas, propane, or outdoor grills. Tap water may require boiling—or stop running altogether—if water lines are damaged or municipal providers lose power themselves.

In addition to the basic supplies like water, food, and hygiene products, flashlights and batteries are an essential resource. The flashlight feature on your phone is the easiest way to kill your battery, which is a scary prospect in a lengthy power outage.

Widespread flash flooding

The number one cause of death in any landfalling tropical system is flash flooding from heavy rains, and most of those flood-related deaths occur in vehicles.

Forecasters expect 5-7+ inches of rain to fall along Idalia's path as it cuts from Florida to South Carolina. This glut of drenching rain will likely cause flash flooding throughout the area, especially in flood-prone areas. There are always roads that flood in storms like this, and there are always people who try to ford the high water anyway.

It's impossible to tell how deep the water is until you're in it and it's too late. It only takes a small amount of standing water to lift a vehicle and carry it away, threatening the live of those in the vehicle and those who have to go rescue them or recover their bodies.

Tornadoes are likely through Thursday

Tornadoes are a hazard with any landfalling tropical system. Supercell thunderstorms are common in the outer bands of a storm as high instability and strong wind shear allow these tiny storms to spin like tops.

Tropical tornadoes happen quickly—sometimes touching down and lifting in between radar scans, only lasting a couple of minutes with very little tornado warning lead time. 

These tornadoes are most likely along and to the right of the storm's path, which places the greatest risk for tornadoes across the Florida Peninsula through Tuesday night into early Wednesday, and across coastal region of Georgia and South Carolina during the day Wednesday into early Thursday.

Take a look at your phone and make sure that wireless emergency alerts are turned on for tornado warnings. These free push alerts are proven lifesavers in tornadoes, and the screeching tone is likely to wake even the soundest sleeper.

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August 28, 2023

Idalia on track to hit Florida as a major hurricane Wednesday

Idalia could grow into a major hurricane as it aims toward western Florida by the middle of the week. The system "should keep strengthening up to landfall," according to the National Hurricane Center (NHC), which is a scary and all-too-familiar prospect for storms hitting the Gulf Coast in recent years.

Widespread damaging winds, flooding rains, and a risk for tornadoes will extend well inland from the point of landfall, likely bringing hazardous conditions to a wide swath of the southeastern U.S. through the end of the week.

Tropical Storm Idalia is taking full advantage of the environment around the system this weekend as it rapidly gets its act together off the tip of the Yucatan Peninsula. The system, which has remained near-stationary for the past couple of days, used the opportunity to improve its structure and gather strength over the region's steamy waters.

The storm had maximum winds of 65 mph by 8:00 a.m. on Monday, and it's likely going to grow into a hurricane during the day as it slowly makes its way north toward the western tip of Cuba.

Lower wind shear and ample warm waters will give the system free reign to strengthen as much as possible over the next couple of days as it heads toward the western Florida coast. The NHC calls for the storm to reach major hurricane status before landfall during the early morning hours on Wednesday.

At this point, the only potential impediment to its strengthening would be the storm's internal structure. If it struggles a bit, or undergoes an eyewall replacement cycle at some point, it will hamper (if not just briefly) the storm's strengthening trend.

Communities along the coast are at greatest risk for life-threatening conditions as Idalia strengthens and heads toward its inevitable landfall early Wednesday morning.

This is a high-stakes forecast, as small shifts in the storm's position or track could have huge implications for folks along the coast. It wouldn't take much of an eastward jog to bring the storm closer to the Tampa Bay area, which would push stronger winds, heavier rain, and a greater surge into the coast.

Source: NHC

The NHC expect a maximum potential storm surge of 7-11 feet along the Big Bend between the Aucilla River and Chassahowitzka, which could happen if the storm's landfall coincides with high tide.

Farther south, we could see a surge of 4-7 feet push into Tampa Bay, which could lead to extensive flooding in this heavily populated metro area. A surge of 2-4 feet is possible farther south in Charlotte Harbor, with tropical storm conditions bringing a 1-3 foot storm surge into the Keys.

The effects of a landfalling tropical cyclone don't stop at the coast. Idalia will maintain its strength for a good while after landfall, bringing hurricane conditions to much of northern Florida, and tropical storm conditions to a large swath of southern Georgia and coastal counties in the Carolinas.

Hurricane watches and tropical storm watches were in effect early Monday morning for much of inland Florida along Idalia's path, and these alerts will likely upgrade to warnings later this morning or afternoon.

Widespread tree damage and power outages are likely as the storm pushes inland, with some communities near the point of landfall and immediately inland potentially going without power for a week or longer.

Flooding rains will pose a significant hazard to much of northern Florida and southern portions of Georgia and the Carolinas through the end of the week. A moderate risk for flash flooding will follow the storm's path inland, with Jacksonville, Savannah, Charleston, and Wilmington potentially seeing more than 5 inches of rain from Idalia by next weekend.

Again, the precise track of the storm will significantly affect where the heaviest rains fall. A jog east or west would push the greatest rainfall totals right along with it. There's also likely going to be a sharp cutoff in rain on the northern edge of the storm.

Flooding from heavy rain is the leading cause of death in any landfalling tropical cyclone. Most flood deaths occur in vehicles. It's a serious hazard that often gets overlooked in favor of the storm's raging winds.

Never try to drive across a flooded roadway. It's impossible to tell how deep the water is until you're already in it, and sometimes the road is washed out beneath the water. It only takes a small amount of water to lift a vehicle and carry it away, risking the lives of those in the vehicle and those who have to conduct rescue or recovery.

There's also a risk for tornadoes through the week as the storm makes landfall. Tornadoes are most likely along and to the right of the storm's path, which will place the greatest tornado risk across much of the Florida Peninsula and coastal sections of Georgia and the Carolinas.

Tropical tornadoes happen quickly, sometimes so fast that they leave little or no advanced warning before they form. Take a moment to check your phone and ensure that emergency alerts are activated for tornado warnings. Lots of folks disable them entirely after one too many ill-timed AMBER Alerts. These push alerts for tornado warnings are proven lifesavers. You don't want to miss an alert that could save you and your family.

The NHC will issue updates on the storm every three hours this week, with full forecasts issued every six hours at 5:00 and 11:00 a.m/p.m. Local National Weather Service offices will handle flash flood warnings and tornado warnings as the storm pushes inland.

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August 26, 2023

Heavy rain, high winds as budding hurricane likely to hit Florida by mid-week

A newly formed tropical depression entering the southern Gulf of Mexico could strengthen in a hurry as it heads toward Florida over the next couple of days.

The National Hurricane Center declared a well-organized disturbance near the Yucatan Peninsula as Tropical Depression Ten on Saturday afternoon.

Dynamics are favorable for this system to get its act together in a hurry. As it is, the storm is almost as impressive as Hurricane Franklin on visible satellite imagery—though initial looks are deceiving when it comes to a storm like this. 

Source: NOAA

Our tropical depression is still building its internal structure, and the NHC expects the system to encounter a favorable environment to organize and strengthen as it enters the eastern Gulf over the next few days.

Wind shear across the region will slacken over the next few days, and bath-like ocean temperatures in the Gulf of Mexico will easily fuel the storm's development if the storm's structure is able to live up to its full potential.

Forecasters aren't holding back on the tropical depression's potential through early next week. The storm, which will earn the name Idalia, could become a hurricane as it approaches western Florida on Monday and Tuesday.

Landfall is most likely somewhere along Florida's Big Bend, but the system is meandering off the Yucatan Peninsula right now, and small changes in the storm's location and path will have large ramifications on where it makes landfall. Anyone in the Florida Panhandle or the state's west coast should closely monitor this storm's progress.

The storm's effects won't remain right along the coast, either. Drenching rains are possible well inland as the storm pushes into the southeastern states, bringing the potential for flash flooding as we head into next week. Downed trees, power outages, and isolated tornadoes are possible along the path of the storm once it makes landfall.

It's likely that the storm's intensity and predicted path will shift over the next couple of days. Remember that the storm forecast maps only apply to the center of the storm—hazardous winds and rain will extend hundreds of miles from the center of the storm.

Watches and warnings will likely be issued for the coast by Sunday or Monday. The NHC issues forecasts every six hours until alerts are issued, at which point forecasters will start issuing updates every three hours.

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August 18, 2023

First-ever tropical storm watch issued for southern California, flash flooding likely

The National Hurricane Center issued its first-ever tropical storm watch for southern California on Friday as Hurricane Hilary continues to gather steam in the eastern Pacific Ocean.

The storm is closing in on scale-topping strength, clocking maximum sustained winds of 145 mph as of the agency's mid-morning update. Hilary is a high-end category four hurricane on the Saffir-Simpson wind scale.

Source: NOAA

It's this formidable strength—and a steady increase in its forward speed—that will give it the momentum needed to survive interaction with land and colder waters to survive into southern California as a tropical storm late this weekend.

Tropical storm watches are in effect for the Los Angeles and San Diego metro areas, as well as Orange County and many locations throughout inland southern California. Winds of 40+ mph are possible alongside the drenching rains, which will likely lead to tree damage and power outages throughout the region.

While the storm will weaken considerably by the time it enters the southwestern United States, it's going to bring a tremendous surge of tropical moisture inland, fueling the risk for prolific rains and catastrophic flash flooding for many vulnerable areas.

We're on track to see widespread rainfall totals of 3-5+ inches through early next week, much of which will fall over deserts and mountains that can't handle downpours that produce a fraction that much rain. Significant and widespread flash flooding is expected throughout the region, along with landslides across vulnerable terrain.

I talked a bit more in yesterday's post about why Hilary is so unusual and what's behind its track toward southern California. If the forecasts hold, this will be a first in living history.

But the fact that this is a rare storm following a rare track is almost secondary to the mammoth flooding threat that's likely to unfold whether or not Hilary makes it to U.S. soil at tropical storm strength. Even if the storm weakens, that vast reserve of moisture aloft isn't going anywhere. This rain is coming. The bullseyes may shift with the storm's track, but much of southern California, southern Nevada, and western Arizona is on track for a copious amount of tropical rains through early next week.

If you live in the region, please take the watches and warnings seriously, and heed the advice of local officials if they issue evacuations in flood-prone areas. Flooding is the single deadliest hazard in any landfalling tropical system.

Never try to drive across a flooded roadway. It's impossible to tell how deep the water is until it's too late, and the road may have been washed out beneath the floodwaters. It takes very little moving water to lift a vehicle and carry it downstream. The vast majority of flooding deaths occur in vehicles, and they're almost always preventable if the driver didn't attempt to ford the water.

Updated at 5:45 p.m. EDT to reflect that the tropical storm watch has been expanded to include Los Angeles.

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August 17, 2023

Southern California faces a serious flash flood threat with Hurricane Hilary

A serious flooding threat will likely develop across parts of California, Arizona, and Nevada beginning this weekend as Hurricane Hilary or its remnants track into the region through early next week.

Every once and a while, the meteorological factors align to make the improbable happen. A tropical system surviving long enough to approach southern California takes a multitude of ingredients falling together just right to come to fruition. 

Regardless of its 'official' title by the time it reaches California, Hilary or its remnants could bring significant, widespread, and life-threatening flooding to California, Arizona, and Nevada by early next week. Folks who live in flood-prone areas need to pay close attention to watches and warnings in the coming days.

Hurricane Hilary rapidly strengthening near Mexico

The National Hurricane Center expects Hilary to reach major hurricane status as it approaches the Baja Peninsula over the next couple of days. Forecasters call for the system to peak as a strong category four storm overnight Friday into Saturday morning before losing steam as it approaches cooler waters.

Hilary will begin picking up speed as it travels farther north, possibly making landfall on the Baja Peninsula on Sunday as it tracks toward southern California. The system—or its remnants—should cross the international border on Sunday night or Monday morning.

Even though Hilary will fall apart soon after landfall, the system's prolific tropical moisture will fuel torrential rains as its remnants push north through California, Arizona, and Nevada through early next week. 

Folks in the west don't see these NHC maps very often unless they're tracking weather back east. The forecast shows the predicted center of the storm at each time step over the next five days. The cone of uncertainty around the forecast points is the historical margin of error in the NHC's forecasts. A storm's center typically stays within that cone of uncertainty about two-thirds of the time.

Heavy rain and gusty winds usually extend hundreds of miles from the center of the storm, so when forecasters say "don't focus on the exact track of the storm," it's a silly-seeming reminder that storms are much larger than a single point on a map. 

What could happen across the Western U.S.

Far and away the greatest threat with this system will be torrential rainfall and widespread flash flooding. This outcome is likely whether or not Hilary reaches California as a tropical storm. 

The vast plume of tropical moisture lofted into the atmosphere by a hurricane doesn't just disappear when the storm starts to fizzle out. We'll see this tropical moisture surge inland across California, Arizona, and Nevada this weekend and continue through Monday and Tuesday.

Such a rich reserve of tropical moisture aloft acts like a reservoir for thunderstorms to tap into, allowing them to produce copious rainfall totals in a short period of time.

This kind of a situation would cause problems in areas where they're used to heavy rainfall. A setup like this across desert areas, urban development, mountains, and lingering burn scars will cause widespread flash flooding, landslides, and mudslides for the duration of the heavy rains.

We're likely going to see significant flooding throughout the region regardless of Hilary's status by the time it reaches the area. The greatest threat for flooding usually falls along the eastern side of a system's track, which would expose the deserts and mountains to the potential for 5+ inches of rain in a relatively short period of time.

Stay alert for watches and warnings if you live in a flood-prone area. Keep multiple routes in mind if you have to drive through areas expecting heavy rainfall. Never try to drive across a flooded roadway. It takes very little water for a vehicle to lose traction and float downstream. It's impossible to tell how deep the water is until it's too late, and the road is sometimes washed out beneath the floodwaters.

Why we're dealing with such an odd situation

Like a flipped quarter landing on its side, Hurricane Hilary seems to have everything working in its favor to bring significant impacts to California, Arizona, and Nevada by this weekend.

Source: NOAA

California almost entirely avoids tropical systems because upwelling off the coast keeps the sea surface here far too chilly to sustain a tropical system. Only two systems in the past century have reached Californian soil as tropical systems—Jennifer-Katherine in 1963, and Nora in 1997—both as weakening tropical depressions.

Nora is an especially interesting case, as it was a powerful hurricane that formed during a strong El NiƱo year and moved along a somewhat similar path as Hilary is expected to follow. The system tracked into the desert southwest as a tropical depression and brought tremendous flooding to the region as it pushed inland.

Tropical systems are rare enough here to count on one hand because the frigid ocean waters rob these systems of virtually all their energy, forcing them to fall apart in spectacular fashion.

However, it seems Hurricane Hilary is on track to exploit as many favorable factors as possible. It's going to run parallel to the Baja Peninsula, allowing the center of the storm to avoid cool water as much as possible.

Source: Tropical Tidbits

It's also riding around the edge of a significant ridge of high pressure building over the middle of the United States. This is the 'heat dome' you've probably heard will roast much of the country east of the Rockies through next week.

You don't even need to look at that upper-level map to see the ridge's influence...just look at the precipitation chart to see where it's going to be hot and sunny, and where all the storms and disturbances will ride the rim of the ridge. (Say that five times fast.)

This forecast from the Weather Prediction Center also does a great job highlighting how Hilary's remnant moisture will continue streaming over the northern Rockies and deep into Canada through next week.

[Satellite Image: NOAA]

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August 6, 2023

Widespread severe storms with high winds to sweep across the eastern U.S. on Monday

Well, that's strange.

It's a little unusual to see such a sprawling risk for severe weather as we approach the middle of August, but a robust system swinging into the eastern United States will trigger multiple lines of severe storms through the day on Monday.

The Storm Prediction Center issued a very large enhanced risk for severe weather—a level 3 out of 5 on the scale measuring the risk for severe storms—stretching from Birmingham to Philadelphia.

Plenty of hot, muggy air parked over the eastern states will provide the fuel needed for thunderstorms to roar through the day Monday, largely sparked by a cold front advancing into this summertime airmass.

Forecasters expect enough instability and wind shear for these storms to organize in a hurry and turn severe. Far and away the greatest threat with these storms will be damaging wind gusts. We're likely to see the storms develop into numerous squall lines, with each one likely capable of producing 60+ mph wind gusts as they push through.

Storms will likely form west of the Appalachians by the early afternoon Monday, steadily pushing east through the late afternoon and evening hours.

The SPC's forecast on Sunday showed a very large area at risk for damaging wind gusts on Monday, with the greatest threat concentrated on the I-85/95 corridor from Birmingham north through the Philly area. There's a decent chance that the strongest storms could approach the D.C. metro area through Monday afternoon and evening.

There's a chance that some of the discrete thunderstorms—the loners that form on their own, away from the interference of nearby storms—could develop some rotation, bringing with them a threat for large hail and possibly a tornado or two.

We could also see little 'kinks' develop along the leading edge of some of the squall lines, bringing the potential for a quick tornado or two embedded within the stronger lines of storms.

Things will calm down once the cold front pushes through, and most folks across Tennessee/North Carolina and northward should enjoy a touch of lower humidity on Tuesday and Wednesday.

A climatology map showing where damaging winds in severe thunderstorms are common on August 7 in any given year. (SPC)

So...why is this strange, exactly? 

August is usually the doldrums when it comes to weather east of the Mississippi River. Around this time of year, the jet stream is typically all the way north in Canada, allowing any low-pressure systems to swirl through the Plains before lifting north of the international border.

That relative lack of an active pattern leaves the eastern third of the country to the whims of tropical systems in the Atlantic or pop-up thunderstorms fueled by daytime heating—those random storms that bubble up where they may, raging for an hour before fizzling out with the loss of sunlight.

But the pattern over the U.S. and Canada in recent weeks has allowed these robust systems to track farther south than they normally would, essentially creating a setup where we have May-like storm systems tracking into the full-blown August heat.

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