Month: August 2019

Hurricane Dorian exploded into a category 4 monster hurricane overnight, and it will next torment the northern Bahamas. From there, it will drift a bit more and then turn north, but exactly where that turn occurs will determine how severe the impacts are for Florida, as well as perhaps for areas farther up the coast. Let’s walk through things.

Now

One look at a satellite loop of Dorian tells you all you need to know about the storm in its present state.

Dorian is nearly a textbook major hurricane as it meanders its way toward the Bahamas. (Tropical Tidbits)

Dorian is menacing, with maximum sustained winds of 150 mph, making it a strong category 4 hurricane on the Saffir-Simpson scale. Over the next 2 to 3 days, Dorian will likely fluctuate in intensity.. But in general, expect it to remain at least a category 3, major storm. It’s not impossible to think Dorian could briefly attain category 5 status at some point. But typically, when storms get this strong, there are various ups and downs in intensification periods that are challenging to predict.

Dorian’s track

In 2016, Hurricane Matthew approached the Florida coast from the southeast. It brushed the coast but never made landfall in Florida, yet it was still a billion dollar storm for the state. In 2017, Irma approached the Keys from the southeast, while it was expected to make a sharp turn north. In that instance, 25 to 50 miles difference in where that turn occurred would mean huge differences in impacts for the entirety of the Florida Peninsula. It did approximately $50 billion in damage in what was not even close to a worst case scenario for the state. And now we have Dorian, which has been threatening a direct hit on Florida, but that has been contingent on the exact timing of a turn to the north. Multitudes of options, including a track into the Gulf or a right turn out to sea have been viable scenarios. The trend today has continued to shift toward more of a Matthew-type “brush,” as Eric discussed yesterday.

Dorian is moving west, as you see from the satellite image above. The latest NHC forecast implies that Dorian will approach the Florida coast and then turn north.

The National Hurricane Center predicts Dorian will turn north either along the coastline and just inland or just offshore. All areas in the cone should prepare for potential hurricane impacts. (NOAA)

We say it ad nauseam, but we really mean it: Do not focus on the implied track of the center here. Focus on the cone. The future track of Dorian will be contingent on the exact strength and orientation of high pressure to its north, as well as the trajectory, strength, and orientation of an upper atmospheric disturbance (trough) in the Midwest and East next week. These are all things that can change subtly in the hours and days ahead, forcing Dorian to track a few miles in one direction or another. Any shift in those expectations would have significant impacts on what conditions are experienced on the coast.

In fact, if you look at the latest spread of European ensemble members from last night’s run, you can see a wide dispersion of possible tracks.

Each line represents a possible track of Dorian’s center (impacts will extend well away from the center) over the next 6 days. While most solutions stay offshore, it’s still a very, very close call. (Weathernerds.org)

Yes, only a handful of members track the storm across Florida now. It’s not the favored outcome, but it remains a possible outcome. Again, this is why we urge folks to focus on the cone.

So Dorian should turn north after hammering the northern Bahamas. The turn north should occur either along the Florida coast or 50-100 miles offshore. Coastal impacts will still be significant, even in a miss. Dorian will generally track slowly north before eventually turning toward the northeast. Again, timing matters here because the Carolinas are in the way. It’s plausible that Dorian makes it far enough west to eventually make a landfall in South or North Carolina. We have a few extra days to iron that out. As Dorian moves north, it should slowly weaken a bit as well.

Regardless of landfall or no landfall, Dorian promises a few things: Rough surf, coastal flooding, potential surge, and beach erosion for the coast from Florida through at least North Carolina. Also, Dorian should bring a healthy amount of rainfall.

Dorian will be another big rainmaker for the coastal Southeast, with 6 to 10 inches of rain along the coast likely. (NOAA)

Rain totals should be about 6 to 10 inches along the coast from West Palm Beach to Cape Hatteras. Higher amounts are possible, and rain could extend farther inland in the Carolinas as well. Conversely, if Dorian does track farther offshore, closer to the right edge of the current forecast cone, these rain totals will be a good bit lower. But the most probable scenario right now suggests heavy rain along the coast.

Barring any significant changes today, we will update you again tomorrow morning.

Lastly, the National Hurricane Center is also assigning about a 20 percent risk of development in the southern Gulf from the disturbance we’ve discussed all week here on the blog.

There is low risk for a system to organize in the southern Gulf, but it should stay south of Texas and well south of Houston, preventing any impacts here. (NOAA)

That is currently likely to travel toward Mexico, and it is unlikely to develop significantly. We should not see any impacts in Houston from this system. There are other systems likely to develop in the far east Atlantic off Africa next week, but none of those looks like a serious concern at this time. The Gulf is expected to turn quieter for a stretch beginning later next week.

In Thursday afternoon’s post on Hurricane Dorian, we called attention to the high uncertainty in the track for the storm—and that remains the case this afternoon. Before discussing this, let’s just note that Dorian has reached Category-3 status, and will likely be a major hurricane at a Category 3, 4, or potentially even 5 level as it approaches Florida on Monday.

The problem for trying to determine where Dorian goes is that steering currents fall apart over the weekend, and so Dorian’s forward speed is likely to slow to a few miles per hour. This means that it could stall, or wobble offshore, before finally getting pulled in some more definitive direction. At some point it will find the western edge of a high pressure system and get pulled north, but the big question is whether that happens 50 or 100 miles off the Florida coast, along the Florida coast, or inland. Here’s the official track forecast as of 4pm CT—they’re basically splitting the difference.

That is a very large cone of uncertainty. (National Hurricane Center)

This afternoon’s ensemble output from the European model suggests that, more likely than not, Dorian’s center will remain off the Florida coast. But we will want to see this model trend continue for another 12- to 24-hours before having too much confidence in such an outcome. Nevertheless, what we are seeing now is a good trend.

More than two-thirds of the ensemble members of the European forecast model now keep the center of Dorian offshore. (Weathernerds.org)

In terms of impacts, obviously it’s much better if the storm stays offshore. But unfortunately, given all of the uncertainty, most of the Florida peninsula, as well as Georgia and the Carolinas need to be prepared for the possibility of high winds and heavy rainfall early next week. Hopefully as the track gets better defined, we’ll be able to clear some areas of significant threats.

We saw a few showers in the area on Thursday, but for the most part it was a much calmer day than Wednesday. Some folks in our area have been bypassed by these showers more often than not lately, and it’s beginning to add up across much of Texas.

Drought is beginning to expand across much of the state of Texas. (U.S. Drought Monitor)

The latest drought update released on Thursday shows about 75 percent of Texas in abnormally dry or drought conditions. In the Houston area, as Eric so aptly described on Thursday, we’ve been playing “rainfall roulette” lately. Fort Bend County? Abnormally dry. Brazos Valley? Abnormally dry or in drought. Across Houston and southeast, it’s been almost comical, with Hobby Airport about 2 inches above normal this month thanks mostly to one big storm on August 19th. Galveston, meanwhile, is almost 2 inches below average for the month. IAH Airport? About an inch below normal.

Over the next couple days it would seem that just a few of us will see downpours, while many will stay dry, so drought will continue as an emerging storyline into September.

Today

Look for a typical summer day today: Sun, clouds, hot, and scattered hit or miss downpours. Rain will be mostly near the coast in the morning, especially toward Matagorda Bay. Showers should migrate inland for a lucky handful of communities in the afternoon. We should reach the mid-90s this afternoon, though it will feel 5 to 10 degrees hotter than that.

Weekend

Both Saturday and Sunday look partly to mostly sunny and hot. Morning lows will start off in the mid- to upper-70s, while daytime highs should easily peak in the mid-90s. Rain chances? The better chance is on Saturday, but even that will just be a handful of isolated showers. I would anticipate a mostly dry weekend.

Read More…

We’ve had a lot of requests from out-of-state readers to continue providing our perspective on Hurricane Dorian—which threatens to make landfall in Florida as a major hurricane in three or four days time. To be clear, there is absolutely no threat to Houston or Texas.

As of 4pm CT on Thursday, Dorian had maximum sustained winds of 85mph, but based upon its satellite appearance it appears likely to undergo a bout of intensification soon. It will likely become a major hurricane within 24 hour, and then should experience more or less favorable atmospheric conditions for further intensification for several days as it passes north of the Bahamas and turns west toward Florida.

In looking at this afternoon’s weather model data, what is particular striking to me is the high degree of uncertainty about where Dorian is going to go by Sunday or Monday. There is, in fact, no guarantee it will even hit Florida. There is a non-zero chance it goes south of Miami, or turns north before reaching the Florida peninsula. A little while ago, I wrote a story for Ars Technica about this uncertainty, which is highlighted in this afternoon’s ensemble output from the European forecast model:

Five-day ensemble forecasts for Hurricane Dorian’s track. (Weathernerds.org)

If you click the image above to enlarge it, the following explanation will probably be more clear. In any case, this plot shows the track of Dorian out to 120 hours, so that means its position as of Tuesday at 7am CT. Notice that there is a remarkable variance in the location of the “center” of Dorian in these roughly four dozen ensemble members. Yes, a reasonable amount of the ensemble members bring Dorian to the coast between Sunday and Tuesday, but some are far, far away. In some scenarios, Dorian turns north before even reaching Florida. This is reflective of the fact that steering currents for the storm are likely to become extremely weak by Saturday or so.

The 4pm CT Thursday track forecast from the National Hurricane Center captures this ambiguity. It encompasses the entire Florida peninsula within the five-day cone of uncertainty.

4pm CT Thursday track forecast from the National Hurricane Center.

This is singularly unhelpful to the residents of the Sunshine State, who are staring down at the possibility of a major hurricane making landfall somewhere along the peninsula in three to four days. The time for preparations and evacuations is now, but it is hard to offer much in the way of specificity about where the worst storm surge, damaging winds, and inland rainfall will occur. Certainly a slow-moving storm will make the latter variable, rainfall, worse.

Matt and I will continue coverage of the storm through the Labor Day Weekend.