Wednesday Hurricane Delta Update

October 7, 2020

Hurricane Delta made landfall near Cozumel and Cancun Mexico early this morning, as a strong category 2 storm is my guess, and it will soon move out over the Gulf of Mexico. Thankfully, Delta's wind speed decreased steadily overnight up until landfall. Delta's future over the Gulf is about the same although models aren't showing quite as much restrengthening and the forward speed has increased a little. Delta is forecast to be a mid category three storm by tomorrow evening and to maintain this strength until it is close to making landfall on the central-western Louisiana coast around Friday afternoon.

As Delta progresses inland Friday and through the weekend there will likely be effects across much of Alabama, especially the central to northern areas, the western Florida Panhandle, and all of Tennessee. Localized heavy rain, gusty winds, and isolated tornado threats will be the main concerns. The National Weather Service will start to highlight any specific risks and risk areas over the next few days.

In the long term, we may need to watch both the Caribbean and the Atlantic off the southeast US for tropical development starting mid next week into the early part of the following week. There's no strong signals at this point but there are some hints at development in these areas. 

This will be it for me for today unless something changes unexpectedly.

Chris

Tuesday Evening Update on Hurricane Delta

October 6, 2020

Hurricane Delta is now a strong category 4 hurricane with 145 mph winds. It is forecast to continue to strengthen to 155 mph in 12 hours, just shy of category 5 strength. The NHC's forecast only covers 12 hour intervals so it's possible Delta could be even stronger at landfall, this possibility is being hinted at by several models. Only 36 hours ago, Delta was a 35 mph tropical depression. That is a 110 mph increase in a day and a half! Rapid intensification like that is extremely rare with only 1 or 2 other storms in the last 50 years gaining that much strength in such a short period of time. The forecast continues to be one where Delta weakens some after making landfall in Mexico, followed by reintensification to category 4 strength, followed by some weakening before landfall in the US. I think we may not know exactly how the final weakening phase will play out until we start to see it happen, although models are in agreement that weakening should occur. The NHC is also reporting the wind field is expected to grow in size as it approaches the coast so even with weakening this will be a significant wind and storm surge event.

The track has shifted to the west slightly again. Now that landfall on the US is within about 72 hours, the forecast cone has narrowed considerably, and I think those of us in Florida can breathe easier. The spread on the track models is about the same as or narrower than the cone (depending on the model) so we can start to feel fairly confident that landfall will be somewhere along the central to central-western Louisiana coast late Friday or early Saturday.

There's not much else to report this evening. My heart goes out to the people in Mexico, a lot of you know what it's like to experience what they are about to go through. Delta will then come close to hitting where Laura made landfall earlier this year...

Have a good evening.

Chris

Delta Now A Strong Hurricane, Continuing to Strengthen Rapidly

October 6, 2020

Hurricane Delta is a strong category 2 hurricane this morning with 110 mph winds, 1 mph away from a category 3. Yesterday I was wrong in thinking that the intensity forecast wouldn't increase beyond category 3 strength. I think the situation is changing so quickly that the models were having trouble keeping up. Delta is forecast to be at category 4 strength with 130 mph winds as it approaches its first landfall on the Yucatan Peninsula tomorrow. I think we may see this increase with the full advisory at 11 a.m. EDT. The language from the 5 a.m. EDT advisory is sobering:

"The hurricane is in the midst of a very impressive rapid intensification episode, having strengthened over 50 kt during the  past 24 hours.  I honestly don't see much that will stop it until it reaches Yucatan..."

You don't see language like that very often from the NHC. The storm is expected to weaken some over Mexico, but then quickly regain category 4 strength over the Gulf. The HWRF model, which the NHC mentions in their 5 a.m. discussion as being a good performer this year, has the storm intensifying to nearly 140 mph over the open Gulf. I think we'll see the intensity forecast for this portion of the track increase as well. The storm is still expected to weaken prior to landfall, with winds forecast in the 100-125 mph range, but I think the details of this are still a bit uncertain.

The track forecast is largely the same, it did shift slightly west a little earlier this morning. I'd be surprised by a large track shift at this point and I think we'll see the landfall point narrow down this evening and overnight. Even so, if you think you may need to prepare for this storm the clock is ticking.

That's it for this morning. I'll send out another update after the 5 p.m. EDT advisory. We'll have two more model runs by this evening and more hurricane hunter data. Hopefully by then there will be a feel for what the ceiling is on the intensity.

Have a good day.

Chris

Monday Evening Update on Tropical Storm Delta

October 5, 2020

As of the 5 p.m. EDT advisory, Tropical Storm Delta is now a 70 mph storm, 4 mph from hurricane strength. The NHC is calling for rapid intensification with the forecast now up to 120 mph 36 hours from now, a mid category 3 storm. It seems the caveats on the intensity forecast I mentioned this morning are being realized. I don't expect the intensity to go up too much more at this point, but the situation is still evolving rapidly. The track forecast is a bit west with this update. The model spread has increased beyond three days, so the NHC mentioned that the uncertainty in the long term has increased as well. I think it will be this time tomorrow or late Wednesday morning before the landfall point starts to narrow down. Delta is forecast to weaken to 100 mph near landfall, but keep in mind that a 100 mph storm that was 120 mph a day before can have a larger storm surge than a storm just reaching 100 mph strength. Regardless of the exact strength, significant wind and storm surge damage is expected. 

That's it for now. The next full update will be at 10 p.m. CDT.

Have a good evening.

Chris

Monday Morning Update on TD 26

October 5, 2020

Note: TD 26 was upgraded to Tropical Storm Delta as I was writing this. While I included the correct forecast map showing the change, I didn't notice the change and thus my discussion refers to the storm as TD 26 throughout.

This morning I've had a chance to take a better look at Tropical Depression 26. The biggest change overnight has been a fairly large shift to the east for the later portion of the forecast track. The storm is expected to head northwest through at least midweek but Gamma could cause a jog to the west at some point. The NHC seems almost surprised at how good the track agreement is between the models. This is good news in light of what we've seen with other storms. There's still some uncertainty on where a strong core will form, which is expected sometime today, and also uncertainty regarding how 26 will interact with Gamma. Both of these could cause shifts in the short term track. Beyond midweek an approaching upper level trough will cause 26 to turn north and then northeast. Where 26 is when this occurs will determine the landfall point.

The intensity forecast is about the same, which shows the storm achieving category 2 strength by day 3 but then weakening prior to landfall. Near shore the Gulf has cooled a bit and this combined with the possibility of increasing wind shear is expected to cause the storm to weaken. There are a few caveats to this however. First, if TD 26 gets its act together quickly today, we could see some rapid strengthening before it has even reached the Gulf. If it can form a good core soon there's not much to limit it in the Caribbean. Second, if it is moving fairly quickly when it reaches the cooler water in the northern Gulf, it may not be impacted much by the lower temps. Third, if there is wind shear, the storm will likely be moving with the shear, this can lessen or even negate the effects it could have on the storm if the shear isn't very strong. The good news is that this morning I'm not seeing any strong model signals that show an intensity above the NHC forecast but we need to watch how this evolves.

Unfortunately the central Gulf Coast is going to be impacted by yet another hurricane. It'll be another day or two before the cone at the landfall point starts to narrow down so if you're in the cone start thinking about preparations. Keep in mind the cone only covers 2/3rds of historical track errors so a track outside the cone is always possible as we saw with Sally. We will see the track bounce around like always but I don't expect any major shifts, we all know how quickly things can change though.

That's it for this morning, have a good week and stay safe.

Chris

PTC 26 Forms in the Caribbean

 October 4, 2020

PTC (Potential Tropical Cyclone) 26 has formed in the Caribbean. The PTC designation is given to systems that are expected to be TCs (tropical cyclones) soon so that the NHC can start issuing advisories for them before they are "officially" TCs. It is expected to become a tropical depression and then a tropical storm in the next 24 hours. Four days out it is forecast to be a category 2 hurricane with 100 mph winds with some weakening possible prior to landfall. You can see the forecast cone below. I haven't had a chance to dig into the forecast, but I understand there's good confidence in the track out to 3 days with increasing uncertainty beyond that.

Since Gamma is still out there I've included the cone for it below, but I think PTC 26 is considered the greater threat to the US at this time. It'll be interesting to see how these two systems in the Gulf will interact with each other.

Here's the 5-day tropical outlook. The yellow areas in the Atlantic aren't expected to be threats to land. 

I'll send out a better update on PTC 26, soon to be named Delta, tomorrow morning.

Chris

Tropical Weather Update

October 2, 2020

Synopsis: I wrote a bit more than I thought I would, so here's a summary: The first system will probably develop into a tropical depression or tropical storm and *could* be a threat to southwest Texas next weekend or the following week, it could also just dissipate over land. The second system needs to be watched also but there's so much uncertainty that it might be mid week before we have a better idea what will happen, if it even develops. Outside the tropics the weather should be mostly nice and boring in the deep south through the coming week.

Here's the 5-day tropical outlook:

The northwest Caribbean continues to be the area to watch for tropical development. The area we've been watching all week now has a 90% chance of development and it is expected to become a tropical depression or tropical storm today or tonight. The future of this system is a bit uncertain. If the storm stays weak in the near term, as is expected, it will continue to move slowly west-northwest and then more westerly. If it were to somehow strengthen significantly, steering currents for a stronger storm could pull it to the northeast across western Cuba and south Florida. As I mentioned, this is not expected. If we go out a few more days to mid week what happens depends a lot on land interaction with the GFS and ECMWF split nicely between two scenarios. The GFS hooks the system to the north around the Yucatan Peninsula and into the Bay of Campeche, avoiding nearly all land interaction. The GFS then has a hurricane form that moves off towards the US/Mexico border late next week or weekend. The Euro takes the system squarely across land where it dissipates over Central America. These aren't the only possibilities but they represent the spread of possible outcomes fairly well. Regarding which will occur is uncertain and depends on where the storm center forms and how strong it is before it gets near land. There is also a front draped across the area with dry air to the north, any developing system is going to have to fight off this dry air.

The next tropical wave, now located more or less south of Puerto Rico has a 30% chance of development over 5 days as it continues west. The general consensus is that this system has the greater potential down the road but a lot of uncertainty remains. Levi Cowan of Tropical Tidbits mentioned last night that this wave could actually split with one piece going north of the Greater Antilles and another going west through the Caribbean. He called the overall situation with this "complex." The current run of the GFS doesn't develop this at all. Because it develops the first system, the outflow from that storm creates unfavorable conditions for the second wave. The Euro brings the second system into the Bay of Campeche late next week where it starts to develop, that is where the model run ends at 240 hours out. As mentioned it has the first system dissipating so favorable conditions are left behind. The ensemble guidance is a bit hard to interpret because there are many runs of two different systems in the same vicinity at the same time. The Euro ensemble has 51 members and the new GFS has 31 so with two systems there is a lot going on looking at one map. The Euro ensemble generally supports the operational model keeping the first system weak and developing the second system in the southwest Gulf. The GFS ensemble has both strong and weak solutions for the first storm so looking out mid to late next week the Gulf is a mess of potential solutions between both systems. It might be mid week before we start to have a better idea what is going to happen and we need to see what the first system does to forecast the next system.

Up here in the mid-latitudes we should have fairly benign weather through most of the coming week (assuming nothing tropical comes our way...). Near the coast we could see some rain Tuesday or Wednesday as some tropical moisture gets pulled up from the Caribbean. Temps should warm by mid week and then we may see a dip by the end of the week and possibly some rain as a front comes through. As a follow up, the last two days where there was a chance of severe weather were a bust. On 9/24 there wasn't a single storm report. On 9/28 there was one wind report in eastern Tennessee.

That's all I have for today. I'll send out another update in the first half of next week. Have a good Friday and a great weekend.

Chris