Sunday Morning Update on TS Sally

September 13, 2020

I wanted to wait until the full advisory from the NHC at 10 a.m. to send out an update this morning. Sally is starting to organize but it still doesn't have convection wrapped around the center very well. Still it has 60 mph winds which isn't too far from hurricane strength. It should continue to organize and strengthen and it is expected to be a hurricane sometime tomorrow. As many of you with a weather radio or weather alerts on your phone will know, hurricane and tropical storm warnings were issued with the 4 a.m. advisory. The forecast intensity has been steadily increasing and it is now for a 90 mph storm at landfall, with the NHC noting that it may actually be a little stronger. The track has been nudged to the west a bit and now shows a southeast Louisiana landfall just after midnight on Tuesday. The forecast has the storm coming in faster now which is good because we may not see a stall over water which would bring hazardous conditions longer and add to the track uncertainty. 

Tornadoes are still a possibility but the Storm Prediction Center has yet to issue any probabilities or designate any severe weather threat areas. While no specific risk has been identified, there could be an area favorable for tornadoes along the Florida Panhandle later today into the overnight hours and we may see the outlook upgraded at some point. Right now, the SPC doesn't see much of a tornado risk tomorrow and overnight into Tuesday. Beyond Tuesday morning there may be a possibility for tornadoes but due to uncertainty in what the environment will be like no specific threat has been identified.

The latest run of the HWRF has cooled a bit on it's forecast, for the last several runs it had been showing a category 3 storm at landfall but as of the 6Z run, which ran a little after midnight, it only shows a category 1 storm. Several of the intensity models still support a category 2 storm as shown below so we'll see if this latest HWRF run is a fluke or the start of a new trend. I'm a little skeptical of this latest run but there may be good reasons for the sudden decrease in intensity, we'll see what the 12Z run shows. The Euro and GFS operational models still don't even show it becoming a hurricane, but I think they're too weak on their forecast.

The track forecast is getting more certain. It is helpful that a stall over the water looks a lot less likely, so that has tightened things up a bit regarding the possible landfall points. There is still quite a bit of spread where the storm may go beyond midday Tuesday, and that could determine where a lot of the rainfall ends up.

That's it for this morning. I think most of the Florida Panhandle can breathe easier now. LA, MS, and AL will likely be dealing with a fairly hazardous storm in a day or so. Have a great Sunday, I'll send out another update late today or tomorrow morning.

Chris

Saturday Morning Update on TD 19

 September 12, 2020

TD 19 is now over land in South Florida and will enter the eastern Gulf later today or tonight. It was very close to tropical storm strength at landfall but has since weakened. It currently has a lopsided structure with most of the convection (storminess) to the southeast over the Florida Straits. It'll be interesting to see if the low level center tries to reform down in this direction. If it does that could change the forecast a bit.

The official forecast from the NHC isn't much different than it was yesterday. They're still forecasting a strong tropical storm to make landfall near the MS/LA border Tuesday or early Wednesday. This is weaker than the intensity model consensus and the NHC has again stated that a hurricane or stronger is possible at landfall. There is some wind shear that could inhibit development so the NHC is keeping their forecast conservative as there's some uncertainty regarding how much this may limit the intensity. The track forecast is still a bit uncertain after two days. One worrisome trend is that the storm is expected for move slowly which could allow more time for strengthening and drop a lot of rain as it nears the coast. Isolated tornadoes are also possible Sunday into Monday across north Florida.

Model guidance is a little more concerning this morning. The HWRF shows a category 3 storm making landfall along the Mississippi coast Tuesday morning. This model can overdo intensity at times so keep that in mind, but sometimes it is right. It forecast Laura's intensity pretty well. I'm not skilled enough yet to know when it is acting up but what it shows is concerning. The GFS brings a category 1 storm into almost the same location but it has the storm grazing extreme southeast Louisiana before hooking north and hitting Mississippi. The Euro brings the storm in a little faster and a hair more to the west as a tropical storm. Yesterday I said the Euro had this as a hurricane, that was a mistake, it had a tropical storm similar to what we see this morning. Either way, I now think the Euro is probably too low on its intensity forecast. There are various other model solution but I think you get the idea. I think it's more likely than not that TD 19 will become a hurricane by late Sunday or early Monday in the northeastern Gulf. I don't have much to say about the track guidance as I think the NHC's cone captures that fairly well. I made a statement yesterday that implied that a stronger storm would be more likely to go west, that is incorrect the way I stated it. In a general sense the longer the storm is over water, the more west it will go. However, a stronger storm will feel a different steering influence than a weaker storm and will turn to the north earlier. So given a certain steering influence, a stronger storm is likely to go more the east and a weaker storm more to the west. Levi Cowan covered this well in his video last night.

Taking a brief look at the rest of the tropics, there remains quite a bit of other activity. Paulette looks to threaten Bermuda as a hurricane in a few days. The red 'x' is still out there moving west, now Invest 95L. Models have cooled somewhat on developing this and a track to sea now looks more likely but not certain. The Lesser Antilles could still see some impacts but I think the US might be out of danger. Another wave that will come off of Africa Monday (not shown) may be the next one to watch.

I'll send out another update on TD 19 later today or tomorrow morning. It's a good time to think about your hurricane plans and get some supplies if you need some. No need to get too excited, but it's good to be prepared. Have a good Saturday.

Chris

TD 19 Forms East of Florida

September 11, 2020

The NHC has started issuing advisories on TD 19 (previously Invest 96L) located east of South Florida, the forecast cone is shown below. TD 19 is only 5 knots away from being a tropical storm so it's likely we could see it get named before it makes landfall near Miami overnight. After that, the storm will cross the Peninsula and enter the eastern Gulf on Saturday. Once over open water it is expected to steadily intensify. The official intensity forecast stops just short of hurricane strength but the NHC cautions that their forecast is conservative and could likely be increased. Regarding the track, the NHC states that there is considerable uncertainty beyond 48 hours and that areas well outside the cone should remain aware.

Computer models are now showing more development than they were this morning. The hurricane specific HWRF, which started to run when this became 96L, shows a strong category 1 hurricane skirting the coast near Pensacola with the storm making landfall near the western end of Dauphin Island, AL early Tuesday. The Euro shows a similar solution but brings the storm in close to the coast off of Panama City and then keeps the storm just off the coast with it making landfall near the MS/LA border late Tuesday as a category 1 hurricane. The GFS takes a weak tropical storm into southeast Louisiana Tuesday morning. Several of the intensity models have solutions showing the storm making it to hurricane strength. Based on all of this I think it is more likely than not that TD 19 will become a hurricane, maybe as early as Sunday night if not by Monday. Fortunately I don't think it will have enough time over open water to strengthen much beyond a category 1 storm. The track guidance seems to be consolidating around a landfall somewhere to the west of the Florida Panhandle, but as mentioned above there is a lot of uncertainty with this right now.

A couple of points of caution. One is that models are just now getting a good look at this so we may see some changes as they start seeing the storm better. We should get some hurricane hunter flights and that will help feed the models with better data. Also, the more time this spends over water the stronger it may become, there's really not much to inhibit its strength. That being said more time over water probably means a track farther west as well.

That's all for today, I'll send out another update in the morning.

Chris

System East of Florida is Now Invest 96L

September 11, 2020

I'm only going to talk about the orange system east of Florida this morning, now designated Invest 96L. The National Hurricane Center has increased chances of development to 40% over the next two days and 60% over 5 days, here is part of their statement:

This system is forecast to move westward at about 10 mph, crossing the 
Bahamas and Florida today and tonight and moving into the eastern 
Gulf of Mexico on Saturday.  Upper-level winds are expected to 
become conducive for development, and a tropical depression could 
form while this system moves slowly west-northwestward over the 
eastern Gulf of Mexico this weekend and early next week.

Levi Cowan explained a lot about this system in his video update last night. Computer models still aren't showing much development from it but he said sometimes models can miss systems like this. Now that it is an invest, the hurricane models such as the HWRF and HMON will start looking at it so we'll see what they come up with. The NHC mentions that a tropical depression could form and I think the most we could expect from 96L would be a tropical storm. Interestingly, the Tallahassee NWS office, which covers the Florida Panhandle east through Walton County, only mentions this system due to the increased rain chances it'll bring to the area. They really don't seem too concerned about tropical development from it.

Have a good Friday and a great weekend. I'll keep you posted on how 96L evolves as well as the rest of the tropics.

Chris 

I want to make a correction to yesterday's (9/10/2020) post. Where I said "although the eastern most system will encounter some wind shear.." I meant to say "western." Sorry about that.

Quick Morning Update on the Tropics

September 10, 2020

Today marks the climatological peak of the Atlantic hurricane season (yay...) and the 5-day outlook doesn't disappoint in this regard. I wanted to provide a quick update (ok, maybe not so quick now that I've written it...), mainly due to the potential for short term development in the Gulf. Two surface low pressure systems, one northeast of the Bahamas and one in the northeastern Gulf, are being watched by the NHC and have been given a 30% and 20% chance of development respectively. Conditions in the Gulf will be favorable for development, although the eastern western (edit: 9/11/2020) most system will encounter some wind shear, but there is very little organization with both systems and they won't have a lot of time over water before they move over land this weekend or early next week. Other than a few hints from a couple of ensemble members models aren't bullish on these. I just don't think they'll have time to really spin up and get going. I think the system near the Bahamas is the one to watch more closely as it looks a little healthier and will have the best conditions, so it's possible we see this develop into a tropical storm in the Atlantic or northeastern Gulf. Right now I'm not too concerned about either but anytime we see low pressure systems starting to form in an area with favorable conditions they need to be watched.

There's nothing new to say about Paulette and Rene. Again it's still possible Paulette tries to sneak in towards the East Coast but I think that's unlikely. Rene is what is fondly called a "fish storm" by some, it's expected to curve out to sea and only bother the fishes :).

I'm getting a little more concerned about the wave coming off of Africa. It is the red 'x' and long red oval in the eastern Atlantic. There are stronger indications that this system may not curve out to sea as it heads west. The GFS, ECMWF (Euro), and Canadian operational models bring a storm into the northern Lesser Antilles and then northeastern Caribbean mid next week. The GFS and Euro ensemble members are somewhat split on this so a track more to the north and out to sea is still a potential solution, although I think a track to the west is slightly favored. We're well beyond the 3-5 day range that I like to stay within for forecasting but I want to let you know how models have been trending. I think it's virtually certain we'll see this wave develop, we just need to watch where it goes after that. I think we'll have a better idea this weekend or early next week.

The orange oval is yet another wave that will enter the Atlantic this weekend, something else to watch...

Have a great rest of the week. I'll send out another update as the picture evolves.

Chris

Tropical Weather Update - September 8, 2020

September 8, 2020

The tropics continue to be active but there are currently no significant threats to the US. Out of that "fruit salad" we had a few days ago, as some like to call it, Paulette and Rene have formed. You can find the forecast cones for both on the NHC website. Paulette has a chance to sneak in towards the East Coast but it looks like it will probably curve out to sea. Rene is not considered a threat at this time and will most likely curve out to sea. The orange area off the Carolinas, now Invest 94L, bears some watching but is not expected to significantly develop.

The red area way out east is a strong tropical wave that will enter the Atlantic on Thursday. This we really need to start watching around the end of the week, but it'll be a week and a half or better before we would get concerned about it. The models have pretty excited about developing it. The GFS, Euro, and others, along with many of their ensembles, show it developing as it moves west. You can see TC genesis probabilities for it below (ignore the other areas). What is concerning is that a track out to sea is maybe less likely for this system, but this is far from certain at this point in the forecast. We could definitely see a storm threatening the northern Lesser Antilles towards mid next week.

We're getting to the time of year where we're going to start getting a regular cycle of cold fronts moving east and we might actually see some cooler weather from one in a few weeks. What these fronts will do occasionally, depending on timing and location, is break down the high pressure over the Atlantic that wants to steer storms to the US. This could allow any storms to recurve to sea away from the US. We're starting to see that now with Paulette and Rene. These fronts can also help pull storms up from the south if they're way down in the Caribbean or spin up tropical cyclones in the Gulf or off the East Coast if they leave some energy behind, they can be a double edged sword.
This season continues to set records, Paulette and Rene are the earliest "P" and "R" storms. We only have four more letters and then we start using the Greek alphabet! Thankfully, even though we've had an above average number of storms, overall they haven't been very strong. Below is a plot of Accumulated Cyclone Energy (ACE) for the season from Colorado State's site and as you can see we're actually a hair behind where an average season would be.

That's all I have for today. I'll have another update around the end of the week once we know more about what this next wave is going to do.

Have a great week.

Chris

Tropical Weather Update - September 4, 2020

September 4, 2020

The 5-day outlook continues to look busy in the eastern Atlantic.There are a few healthy waves that need to be watched, the orange and red "x's" (the orange 'x' is Invest 91L), and then another wave that will enter the Atlantic on Sunday, the eastern orange area. I think we will see development in this region early next week but there is a lot of uncertainty on timing and location. The good news is that there are no serious threats to the US soon, although the Lesser Antiles may see something mid to late next week. Also, not shown is a wave in the western Caribbean that forecasters have been watching, but doesn't show any strong signs of development, for now just know it's there.

The forecast has two major issues that are driving a lot of uncertainty. One is that those three orange and red areas along with a few other waves are expected to interact. Where, when, and how that occurs is mostly unknown so until it plays out we won't have a good idea of where a storm, or multiple storms, may form. We're probably looking at the Monday/Tuesday time frame before this settles and we start to see serious development. What the models seem to agree on is that the red 'x' will pinwheel around the leading orange 'x' and become the leading system (leading as in more western, not necessarily stronger). After that, models disagree on where the dominant development will occur. The Euro develops the red 'x' once it becomes the lead system and then a wave coming off of Africa next Thursday. The GFS doesn't do much with the first two and instead develops the trailing orange area that enters the Atlantic Sunday. The European ensemble isn't too crazy about any of these and instead tries to develop a wave coming off of Africa next Thursday. The GFS ensemble tries to develop the red 'x' once it is in the lead and then also the trailing orange area. This is neat to see in the models, so I've shown the Euro and GFS below, but I'm telling you all this to highlight the uncertainty. We know something is going to happen, just not where or when.

The other forecast issue is regarding where these storms go if they do form. Right now, a track out to sea away from the US looks possible but there is debate whether the mid term forecast is correct. We've had a high pressure sitting in the western Atlantic that has steered a lot of the storms we've had to the west into the US. This is what happened with Laura. The models are showing a strong front (for this time of year) coming through and breaking down this high, allowing potential storms to escape to sea. The debate is that a lot of forecasters aren't really buying into the idea of this strong front. So if this doesn't occur then steering conditions could be such that potential storms stay on a more westward track, again threatening the US. It'll probably be later next week before we get a better feel for what will happen with this.

To sum things up the Atlantic is busy and we need to keep watching. I think we will see one or more storms develop in the next 5-10 days but it'll be early next week before we have a feel for where development will occur and maybe mid-week or later before we know if the US is at risk.

I don't mention it a lot, but all of these emails get posted to Twitter @DeepSouthWXUS and my blog: https://www.deepsouthwx.com/. There are also some weather maps on the blog and links to other resources. The models shown today are from Levi Cowan's great site: www.tropicaltidbits.com. He also does excellent video updates on YouTube when there are storms that we need to start watching here in the US.

Have a great Labor Day weekend. I'll send out another update early next week.

Chris