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Invest 99L Finally Develops Into Tropical Depression 9 in the Florida Straits

By: Jeff Masters 12:11 AM GMT on August 29, 2016

After spending ten days in meteorological limbo-land frustrating forecasters as an “Invest”, 99L finally developed into Tropical Depression Nine, confirmed a NOAA hurricane hunter aircraft late Sunday afternoon. But the storm isn’t done perplexing us yet—the model predictions for the future intensity of the storm remain wildly divergent, even if we now have growing confidence that this storm will track into the coast of Florida north of Tampa on Thursday.


Figure 1. MODIS visible satellite image of Tropical Depression Nine (formerly 99L) forming in the Florida Straits on Sunday afternoon, August 28, 2016. Image credit: NASA.

Satellite images on Sunday evening showed a steady increase in the intensity and areal coverage of TD 9’s heavy thunderstorms, though Key West radar showed only a few spiral bands trying to form near the center. The depression is not likely to organize quickly, as it was dealing with wind shear that was a moderately high 15 - 20 knots. TD 9 was also struggling with dry air, as seen on water vapor satellite imagery. Sea surface temperatures (SSTs) remained favorable for development, though, near 30 - 30.5°C (86 - 87°F).


Figure 2. Total rainfall from Tropical Depression Nine as of 8 pm EDT Sunday, August 28, 2016. Rainfall amounts of 2 - 4 inches were common over Cuba.

Track forecast for TD 9
There is now model consensus among the GFS, European, HWRF and UKMET models that TD 9 will continue on its current west-northwest track through Monday, slow down and stall out in the central Gulf of Mexico on Tuesday, then get caught in the steering flow of a trough of low pressure passing to its north on Wednesday. These steering currents should bring TD 9 to a landfall on the Florida coast north of Tampa on Thursday. In their 5 pm EDT Sunday Wind Probability Forecast, the highest odds for getting tropical storm force winds of 34+ mph from TD 9 were 26%, 24%, and 22%, respectively, for Apalachicola, Panama City, and Cedar Key, Florida. Tampa was given 18% odds.

Intensity forecast for TD 9
The SHIPS model on Sunday afternoon predicted moderately favorable conditions for intensification, with wind shear falling to a moderate 10 - 15 knots, Monday through Wednesday. SSTs will be a very warm 30°C (86°F), and mid-level relative humidity was predicted to be a reasonably moist 65 - 70%. However, the usually reliable European and GFS models showed little to no development of TD 9 in their latest 12Z Sunday (8 am EDT) runs. Our best intensity model, the HWRF model, had TD 9 rapidly intensifying into a strong Category 2 hurricane just before landfall. Other intensity models like the DSHIPS and LGEM models had TD 9 as a borderline Category 1 hurricane at landfall. This storm’s history has been to under-perform, so NHC’s conservative forecast of a 50 mph tropical storm at landfall was a reasonable first guess, given the storm’s weak showing in the GFS and European models. But TD 9 is hiding its cards—still—and could easily be an intensifying hurricane at landfall. The latest 18Z Sunday forecast from the GFS model had TD 9 about 5 - 10 mph stronger than in its previous run. I support a forecast of TD 9 being a strong tropical storm near hurricane strength at landfall—70 mph winds—until the models come into better alignment.

Bob Henson had a detailed summary of the action in the rest of the tropics in his 2 pm EDT Sunday post. We’ll be back Monday morning with a fresh look at the tropics.

Jeff Masters

Hurricane

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

1001. Patrap
Earlier,



Where's the COC? I'm not even seeing this on radar
1003. ariot
Quoting 994. TROPICALCYCLONEALERT:

I am taking the risk of posting long term images. Please do not ignore me for posting them.



I don't mind these at all, unless they are posted in the thick of a landfall.

But for us non-model geeks, it is always best to post the # of hours out and the NAME or number of the storm the weather model is describing.

Otherwise, I'm like zooming and wondering WTF it is.

Cheers.
Something to note with TD9 is that the presence of a weak upper anti-cyclone seems to be attempting to develop near the center for the first time. This can be seen by some outflow of the CDO on the south side. This is a sign of improving structure and likely some further strengthening.

At the same time, a ULL off the east coat of FL and one in the western gulf are going to make it tough for TD9 to find a sweet spot for more ideal development. Intensity forecasting is still very hard. I'm going with a a similar strength system as the NHC and a similar point of landfall for now.
Quoting 961. wadadlian:


Heading where??!!


I believe the Senior Bloboligist was referring to the next system to come off West African coast heading west. We will have 10-14 days to figure out where it will end up going.
1006. FOREX
Quoting 997. StormTrackerScott:

Very good chance of this getting past 90mph while nearing the FL West Coast. Could even make a run for cat. 3.
Latest NHC said unfavorable winds will inhibit intensification in a couple of days.So no reason to move cone Westward as someone else asked earlier and doubtful it will get stronger than CAT 1.
1007. OhNoLa
RE: Katrina's wind damage and whether the NOLA NWS office's warnings were over the top. I lived in the Riverbend area at the time of K and my house backed onto Leake Ave meaning there were no buildings between my house and the other side of the river. My house caught the full brunt of the wind and after the storm the adjuster could see how the force of the wind slightly shifted the house, a shotgun double. One of my brothers lived in corner house in Old Gretna and he could feel the wind shaking his place.
As to "overwarning" on the morning of the 28th, the storm had winds of 175 and it was sheer fortune that it weakened when it came ashore.
Quoting 997. StormTrackerScott:

Very good chance of this getting past 90mph while nearing the FL West Coast. Could even make a run for cat. 3.


no trough will shear him. am thinking strong TS/Minimal Cat 1
1009. Patrap
Quoting 1002. MobileAlabama:

Where's the COC? I'm not even seeing this on radar


Cuz she is over the horizon even on .50 elevation from Key West.

Quoting 1002. MobileAlabama:

Where's the COC? I'm not even seeing this on radar

I was about to ask that same question and to me it looks like it is slowed down or stopped moving all together. I just don't see it!
Quoting 997. StormTrackerScott:

Very good chance of this getting past 90mph while nearing the FL West Coast. Could even make a run for cat. 3.


NOOOOOOOOOOOO NOOOOOOOOOOOO NOOOOOOOOOOOOOOOOO, Tropical Storm...ok, Cat 3=NOOOOOOOOOOOO!
1012. GatorWX
Quoting 980. HighOnHurricanes:



No, I hear that all the time too and its just not fair. However, there was SUCH a focus on Tampa and ending its Hurricane drought, the super skinny forecast cone, and add in the RI that morning, and you can understand why many people from Port Charlotte down S may have felt caught off guard with Charley.

On that note, I was working in Naples at the time, and my boss got a frantic call at 7am the morning of telling him to go into work (we had already been given the OK to close) and get the building ready for possible hurricane conditions. We had already done it the night before, because you just never know.


I'd say the media was much to blame too. I do remember the NHC seemed to put much more emphasis on cone rather than the center line afterward. Either way all affected areas were under a warning well in advance. I feel it was as much a complacency factor with regards to the public. We don't get too many big storms in this part of FL. Most people that live in Pt Charlotte/PG/Ft Myers were not here the last time a biggen rolled through, Donna, so there was no direct analog to Charley, in their minds. Now, much of the public is much more aware, I assure you. Charley was a big deal here in my little area! At the time, the 2nd costliest storm in US history after Andrew. We all know what happened in the years since.
1013. Patrap
Storm Relative 1 km Geostationary Visible Imagery

Click image for loop

1014. GatorWX
Quoting 1004. Jedkins01:

Something to note with TD9 is that the presence of a weak upper anti-cyclone seems to be attempting to develop near the center for the first time. This can be seen by some outflow of the CDO on the south side. This is a sign of improving structure and likely some further strengthening.

At the same time, a ULL off the east coat of FL and one in the western gulf are going to make it tough for TD9 to find a sweet spot for more ideal development. Intensity forecasting is still very hard. I'm going with a a similar strength system as the NHC and a similar point of landfall for now.


Nullschool has been showing it for some time, but it's always been w of the coc amd inducing shear, as it is now. The gfs seemed to want to merge it with 09 as it stalls, last I looked.
1015. 900MB
Quoting 1010. Stormtracker28:


I was about to ask that same question and to me it looks like it is slowed down or stopped moving all together. I just don't see it!


Just under NW part of convection from what I can tell. Check Patrap's post #1013
Quoting 1012. GatorWX:



I'd say the media was much to blame too. I do remember the NHC seemed to put much more emphasis on cone rather than the center line. Either way all affected areas were under a warning well in advance. I feel it was as much a complacency factor with regards to the public. We don't get too many big storms in this part of FL. Most people that live in Pt Charlotte/PG/Ft Myers were not here the last time a biggen rolled through, Donna, so there was no direct analog to Charley, in their minds. Now, much of the public is much more aware, I assure you. Charley was a big deal here in my little area! At the time, the 2nd costliest storm in US history after Andrew. We all know what happened in the years since.



I disagree, the local meteorologists called that turn by Charley towards Lee/Charlotte county shortly after it came off the coast of Cuba, and they were persistently telling people to be ready 48 hours out. Only those who watch nothing but TWC weren't warned far enough in advance. Me and my neighbors were prepared when the storm hit.
1017. Patrap
Cat3, cmon Scott.
1019. Patrap
Best look in the Dvorak pickle,but still askew from the center.

Wind shear is still a problem and will prevent any rapid spin up into RI. Conditions aren't ripe for this to turn into a hurricane. Organization should increase through the afternoon as TD9 moves over improving shear conditions to the west. Once 99L is over the Gulf and away from Cuba, we should see tropical storm designation tonight or tomorrow morning. Unless shear greatly reduces off Florida's west coast, this should be a manageable storm.
1021. BayFog

Cat 1 Lionrock, degrading off Japan, caught between two large upper level troughs, one coming off Asia, the other digging northwest of Hawaii. Lionrock forecast to arc back into northern Japan as a tropical storm.
JeffMasters has created a new entry.
Quoting 1015. 900MB:



Just under NW part of convection from what I can tell. Check Patrap's post #1013

Thanks
1024. Xulonn
moved to new blog...
85.5N, 23.2W (Aprox)Moving 280degrees (W).
1026. Grothar
Getting that "coma" shape

Quoting 1007. OhNoLa:

RE: Katrina's wind damage and whether the NOLA NWS office's warnings were over the top. I lived in the Riverbend area at the time of K and my house backed onto Leake Ave meaning there were no buildings between my house and the other side of the river. My house caught the full brunt of the wind and after the storm the adjuster could see how the force of the wind slightly shifted the house, a shotgun double. One of my brothers lived in corner house in Old Gretna and he could feel the wind shaking his place.
As to "overwarning" on the morning of the 28th, the storm had winds of 175 and it was sheer fortune that it weakened when it came ashore.


My sister lived in Algiers right behind Brechtel Park and Lakewood golf course. Their roof was completely stripped and their garage collapsed, all from wind damage.
1028. Patrap
24.5N 84.7W


By my look here.

Why do most people on here want a hurricane to come their way???
Quoting 1028. Patrap:
24.5N 84.7W


By my look here.



Agree.
1031. GatorWX
Quoting 1016. efallon28:



I disagree, the local meteorologists called that turn by Charley towards Lee/Charlotte county shortly after it came off the coast of Cuba, and they were persistently telling people to be ready 48 hours out. Only those who watch nothing but TWC weren't warned far enough in advance. Me and my neighbors were prepared when the storm hit.


Regardless, I wouldn't blame the NHC for any uncertainty. We were warned and had people read the discussions at the time, I'm sure it was indicated what could happen with a system parelleling the coast. There were a couple local mets that called the turn before the NHC did, officially, but from what I remember, this was not long before Charley intensified into a cat 4. Again, regardless..
If the Tutt over Florida retro-grades to the East, TD9 might have a little more breathing room but the loops currently show otherwise with it edging into the Gulf a bit; likewise, the TUTT cell in the Western Gulf is not retro-grading much either to the West and TD9 is caught in the middle: this will enhance convection and t-storms but hinder significant development past a TS or low-grade Cat 1 IMHO.




Why are we dwelling in the past with Charley and Katrina? We have something to look at today. Not trying to be disrespectful just sayin. It's distracting.
Quoting 1029. Alandrea:

Why do most people on here want a hurricane to come their way???


Drama and adrenaline.
Way too much dry air (blue sky) over the Northern Gulf Coast, unless that changes nothing is coming here of any consequence....
Quoting 1029. Alandrea:

Why do most people on here want a hurricane to come their way???

I like classic cars, so I go to car shows to see them. This is a weather blog that tracks severe weather, like hurricanes, so people come here looking for severe weather. I am sure they do not want the death and destruction, just the might and power that mother nature can conjure up. As far as "come their way"? I guess those want to see it first hand. Some, like me just want to be informed, and sometimes entertained.
1037. Patrap
Quoting 1026. Grothar:

Getting that "coma" shape




Quoting 1034. mojofearless:



Drama and adrenaline.


Yes, I forgot about the DRAMA!
Quoting 1032. weathermanwannabe:

If the Tutt over Florida retro-grades to the East, TD9 might have a little more breathing room but the loops currently show otherwise with it edging into the Gulf a bit; likewise, the TUTT cell in the Western Gulf is not retro-grading much either to the West and TD9 is caught in the middle: this will enhance convection and t-storms but hinder significant development past a TS or low-grade Cat 1 IMHO.








LOL look at all that dry air i the western Gulf and coming down into Louisiana in the upper levels of the atmosphere.....as long as that continues 99L is not going to do much. Conditions off of Florida's Gulf Coast are marginally better....
Quoting 1003. ariot:



I don't mind these at all, unless they are posted in the thick of a landfall.

But for us non-model geeks, it is always best to post the # of hours out and the NAME or number of the storm the weather model is describing.

Otherwise, I'm like zooming and wondering WTF it is.

Cheers.

Ok I was worried because some people put me on ignore for doing this yesterday. It was greatlying unappreciated.
1041. THL3
Quoting 1026. Grothar:

Getting that "coma" shape




Is that different from the "?" shape.
Quoting 950. CaribBoy:



I want it :)

Be careful what you ask for
Quoting 1026. Grothar: Getting that "coma" shape

Jumbo shrimp cocktail
Quoting 1040. TROPICALCYCLONEALERT:


Ok I was worried because some people put me on ignore for doing this yesterday. It was greatlying unappreciated.



removes ignore ;-)
Quoting 1027. SavannahStorm:



My sister lived in Algiers right behind Brechtel Park and Lakewood golf course. Their roof was completely stripped and their garage collapsed, all from wind damage.

Algiers faired well during Katrina, I had no damage. I actually had more damage from Cindy, but that was because a tree came down on the roof.
1046. Ed22
Quoting 1013. Patrap:

Storm Relative 1 km Geostationary Visible Imagery

Click image for loop


If Tropical Depression Nine rapidly intensifies cat 3 isn't out the question.
1047. A4Guy
Quoting 1026. Grothar:

Getting that "coma" shape




Comma, maybe?

"Coma" is the state we are all in after watching this thing for 10 days.
Quoting 969. HoleintheSky:



Long-time lurkerholic here. Just wanted to chime in on this. Went through the eye of Camille about 100 miles inland in Misssissippi, and still have family in the same spot. Hard to believe, but the wind damage from Katrina was worse than from Camille.
Thank you for chiming in. Did you know in Hawaiian your handle would be "Pukalani"? (add: Better translatable from the Hawaiian as "Hole in the Heavens.")
Have a good one.
:)
Quoting 1047. A4Guy:



Comma, maybe?

"Coma" is the state we are all in after watching this thing for 10 days.
Perhaps 99 / 09 has awakened from its coma.
Quoting 1025. CaneHunter031472:

85.5N, 23.2W (Aprox)Moving 280degrees (W).


At 85.5N, does that put the North pole inside the cone?
:)
Quoting 984. CaneHunter031472:



Anywhere in that vicinity (Very low confidence) I'm not the one indicating it, the NHC is. It will probably change, so all we can do at this time is to keep an eye on things.


Probably about the worst place on the West Coast of Florida to get hit by a major hurricane would be just north of Tampa Bay. Imagine Katrina coming in from the WSW/SW with landfall and pushing a 27.75' storm surge, or even a "regular Cat 3" with a storm surge of 9' to 12' up Tampa Bay? That would be devastating!
Keep them shields powered up!

Read an article about Tampa being most vulnerable metro area in USA for damage from storm surge.

Link
Quoting 1034. mojofearless:



Drama and adrenaline.


They need to be careful what they wish for, we went through Charley and let me tell you I'd rather not have that happen ever again.
Quoting 1055. RampagePCFL:



They need to be careful what they wish for, we went through Charley and let me tell you I'd rather not have that happen ever again.

I agree, I live in Jacksonville and we really had a lot of damage from Charley then Frances then Jean.. I was with out power for 10 days during one of those storms.