Upcoming week - June 25-July 1

[Andrew92]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

Evaluating last week

The first two weeks were very good. This past week was not so successful. For one thing, I didn’t predict Invest 95L to develop further, and it not only became Chris but even became a hurricane briefly. Now I never would have predicted a storm that intense to begin with anyway, but as it stands, not predicting any development for this system was simply a botched prediction.

However, I did have kind of a handle that something would form in the Gulf of Mexico coming into the weekend. In fact, the timing for intensification into a tropical storm for Saturday afternoon or early evening was spot-on, with the first advisory as a 50-mph storm at 5 PM. But I was thinking this would be further west, closer to Mexico and Texas, not near Florida. The motion I predicted was also northwestward, but Debby (would have been Chris if not for Invest 95L) decided to go slowly northeast. The system is very broad as anticipated, and the primary threat of heavy rain has been warranted – again, in the wrong location. But surf has also proven to be a major factor in Florida today, but then again Debby has also gotten a tad stronger than I expected, possibly furthering that effect. I had predicted peak intensity of 40-50 mph, but it is currently at 60 mph instead.

All in all, this was a week for the birds. But you know something? Remember when I had that dream of Chris out in the Atlantic, and Debby in the Gulf of Mexico threatening Florida? Why did I not listen to that? If I had gone with that past dream as part of my analysis, I may have had more bias, but my grade might have been about an A- or so (since I never would have expected a hurricane from Invest 95L/Chris, docking me from an A). But for not listening to my intuition (silly as it sounds) and giving in to models that failed me… OK this week was difficult but my grade is still a D.

Debby continues to look like a difficult storm to predict. I will do my best for this new week.

Current situation and analysis

As mentioned, Debby is a broad, disorganized tropical storm, gathering maximum winds of 60 mph. It is currently stationary but generally drifting very slowly northeast toward the Florida Panhandle, dumping heavy rainfall and cause lots of beach erosion along the Florida Gulf Coast. Models are still in wide disagreement over the path of this complex storm. The GFS has been doing a very good job in taking it to the northeast so far, whereas other models have taken Debby further west, into Texas even. Those models have shifted significantly eastward, including the seemingly trustworthy Euro, and only the HWRF does not take Debby into the Florida Panhandle. Due to weak steering currents, it may take until Tuesday or Wednesday to reach the coast, suggested by all but the GFS model, which quickly takes it across northern Florida, into the Atlantic, and then skirting the East Coast. There is merit to this, with a ridge of high pressure that could steer Debby in that direction towards the jet stream. However, as shown in Debby’s current and past motion, that steering flow is weak. This is due to an upper level low in the western Gulf of Mexico, and a second area of high pressure in the Great Plains. The Euro, for what it’s worth, stalls Debby, has her striking the western Panhandle, and then heading into Alabama and Mississippi. But this model continues to shift further and further east; that is the trend. The trend is your friend, after all.

The intensity forecast is also, as usual, very problematic. The SHIPS model follows the GFS model, which has done the best with Debby so far, and peaks it out at about 65-70 mph, as does the National Hurricane Center. The trend with models has also been a weaker storm overall, from a healthy category 1 hurricane to a tropical storm at landfall. The low-level center and the mid-level center have appeared to de-couple, which could cause at least a lag in intensification, if not some weakening. The storm is still also very sheared, with little convection near the storm’s center. Lots of dry air in the Gulf of Mexico has also contributed to this disorganization, and even the stronger storms east and north of the center have weakened because of this. This dry air is making it hard for any convection to really get going near the center of circulation. The pressure earlier today was 990 mb, but has risen to 991 mb since then. Another hindering factor is with the slow motion, Debby may churn up cooler waters in an area where the water is shallower, closer to the coast, and thus having lower oceanic heat content. At minimum, this would slow intensification, if not halt it altogether.

Elsewhere, some models are trying to spit out another system off the coast of the Carolinas. But if Debby heads in that direction, that storm may just wind up being her when all is said and done. But if Ernesto were to come from it, it seems that the steering flow would take it east and northeast, away from the East Coast.

Recent history

Since 1960, these storms have developed and/or occurred during the last full week of June:

Brenda in 1968 (already active)
A subtropical storm in 1974
Amy in 1975
Bret in 1981
Bonnie in 1986 (already active)
Allison in 1989
Ana in 1997
Bill in 2003
Bret in 2005
Alex in 2010
Arlene in 2011

Eleven storms this upcoming week shows the tropics are flexing their muscles a bit more this last week of June. But only three of these storms were hurricanes: Brenda (out in the open Atlantic), Bonnie (in the western Gulf of Mexico, and hit Texas), and Alex (also in the western Gulf of Mexico, hit northern Mexico). Coming close at 65-70 mph were the 1974 subtropical storm (in the eastern Gulf of Mexico, hit Florida), Amy (out in the Atlantic), 1981 Bret (hit the Mid-Atlantic states), and Arlene (in the western Gulf of Mexico, hit Mexico).

Therefore, one thing of note is that the stronger storms tend to congregate either in the Gulf of Mexico, or over the open Atlantic, this upcoming week. However, this trend is true of the less intense storms, as Allison, Bill, and 2005 also occurred in the Gulf of Mexico, and Ana was off the East Coast. When looking at hurricanes, the best bet appears to be in the western Gulf of Mexico. But with such a small sample size, that is little assurance. On another hand, no storms in the satellite era during this last week of June were weakening upon reaching land from the Gulf of Mexico.

Also of note is also how many hurricanes have hit Florida in the month of June since 1960. Only Alma in 1966 and Agnes in 1972 have done the trick, both as category 1 hurricanes.

So what does this all tell us?

Debby is as difficult as ever to predict, both in track and intensity. The track is only very slowly coming together, but the Florida Panhandle is the most likely target. But how long it takes to get there remains just one of the 64,000 dollar questions. The GFS takes Debby into Florida and out of the picture quickly. But Debby is currently crawling, and numerous models still stall this storm out, perhaps a bit too much, before eventually striking the Panhandle by about Thursday. It seems like the GFS is too fast, but landfall on Thursday also seems too late. I am thinking Debby will strike sometime in the middle, on Tuesday or Wednesday.

Another tough question is how strong Debby will get. Well, with Debby as sheared as she is, and perhaps even de-coupled, intensifying will be difficult. Oceanic heat content is also going to decrease as it passes over shallow water. With a slow motion possible, upwelling could very much keep Debby in check from intensifying too much. But lots of dry air may make these other factors just not matter, with the strongest storms east of the center of circulation weaker than before. Finally, history suggests the odds of a hurricane at landfall in Florida are very slim, with only two in the satellite era doing so in June, both as category 1’s. When everything is put together there, I have a slightly easier time believing Debby will strike as a decent tropical storm.

The Prediction

That last section could have just about been the prediction as a whole! But with a lot of variables and models in disagreement, this is a very low confidence forecast. I predict Debby to continue to continue to drift slowly northeast into Apalachee Bay by Monday night, gathering maximum winds of 50-60 mph. Debby will then start to accelerate a little on Tuesday, making landfall that evening with maximum winds of 40-50 mph in an area between St. Marks and Cedar Key. I believe that Tropical Storm Debby has indeed peaked in intensity, thanks to all the dry air, coupled with the lower oceanic heat content to come. Through this time, heavy rain will still continue to pummel pretty much all of Florida, and beach erosion will continue all along the Gulf Coast as the storm meanders in the area. Debby will also continue to spawn some tornadoes throughout the peninsula, trending further north as she gets closer to the coast. After making landfall, Debby will quickly weaken to a tropical depression by Wednesday afternoon, and then emerge into the Atlantic somewhere along the Georgia coast. Debby will then get caught in the jet stream and accelerate out into the open Atlantic, staying south of the Carolinas while becoming extratropical on Thursday. Confidence is 30% - please do NOT treat this as an official prediction! Please listen more closely to the National Hurricane Center for official forecasts, and your local authorities for what to do in the event this storm affects you, whether significantly or very little.

Elsewhere, I predict no tropical cyclone development or activity. Confidence is 90%.

-Andrew92

[Andrew92]

I don't think there will be anything at what would be an 11 PM advisory, so let's evaluate.

Last week was, to date this season, my lowest confidence prediction. There was good reason behind that, as Tropical Storm Debby was meandering in the Gulf of Mexico and numerous models gave various solutions for what she might do. The Euro insisted on some sort of a westward turn, as did the HWRF. The Canadian model trended eastward, but not as far as the GFS. These models also practically stalled Debby over the Gulf of Mexico for several days. The GFS never really deviated from its stance, taking her into Florida, before any of the other models, and then off the East Coast out to sea. The GFS did the best job out of all the models… and fortunately for me was the model I generally sided with! In picking that model, I made out a not perfect, but very good, weekly prediction on one of very low-confidence.

Let’s run through. First, I predicted Debby to strengthen no further than where it was already at 60 mph, due to dry air entrainment and shallower water as she approached Apalachee Bay on Monday; all of this happened. The landfall location was also inside my tight window of between St. Marks and Cedar Key. I even predicted weakening before landfall on Tuesday evening. Landfall occurred at the 5 PM advisory on Tuesday evening, with maximum winds of 40 mph (I predicted 40-50 mph). Therefore, this was also nailed to near perfection. Rainfall primarily, but also tornadoes and beach erosion did remain major effects from Debby until she passed through Florida. Now there were a few minor holes in my prediction. First, I predicted Debby to weaken to a tropical depression on Wednesday, but it happened Tuesday night shortly after landfall. I also predicted Debby to re-emerge into the Atlantic over Georgia, instead of near St. Augustine, Florida. Finally, I predicted Debby to become extratropical on Thursday, but she de-generated into a low on Wednesday evening instead. Given that the difference between my predictions and what actually happened with these parts was barely off in all cases, and with minimal effect overall, this was still a very well put-together prediction. This is especially when considering Debby was a very difficult storm for many professionals and models, let alone an amateur like me, to predict.

On top of doing very well on a low-confidence prediction with Debby, I correctly predicted no other tropical developments elsewhere. There was Invest 97L, but it has since faded, and Invests do not count as developments anyway. My prediction wasn’t perfect, but the errors were pretty minor in the grand scheme of things. I have had some low-confidence predictions before, and many did not fare well. However, this one is probably my best one yet. My grade for this past week is an A-.

First week of July coming right up.

-Andrew92