Ex-Dorian Attempting a Comeback off the Florida Coast

By: Dr. Jeff Masters , 1:44 PM GMT on August 02, 2013

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After a long trek over the Atlantic Ocean from the coast of Africa, the remains of Tropical Storm Dorian (now called Invest 91L) have finally arrived at the shores of North America. Ex-Dorian is nearly stationary, and is situated over the Northwestern Bahama Islands, just off the coast of Southeast Florida. Satellite loops and Melbourne, Florida radar images show that ex-Dorian has only a limited amount of heavy thunderstorms, which are not well-organized. There does appear to be a surface circulation center trying to form just north of the storm's heaviest thunderstorms, about 70 miles east of Vero Beach, Florida. However, dry air to the northwest, as seen on water vapor satellite loops, is inhibiting development. WInd shear is moderate, 10 - 20 knots, but is expected to rise to the high range, 20 - 30 knots, by Saturday morning. Ex-Dorian is expected to move slowly northwards and then north-northeastwards on Saturday. This motion will get ex-Dorian tangled up with a cold front that extends from Northern Florida northeastwards, just offshore from the Southeast U.S. coast. Before it merges with the front, ex-Dorian has some potential for regeneration into a tropical depression, and in their 8 am Friday Tropical Weather Outlook, NHC gave ex-Dorian a 30% chance of becoming a tropical cyclone by Sunday. Ex-Dorian will likely bring heavy rains to the Northwest Bahamas on Friday, and these heavy rains may also clip the coast of Southeast Florida. However, the bulk of ex-Dorian's rains should stay offshore.


Figure 1. Morning radar image of ex-Dorian from the Miami radar.

Jeff Masters

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Quoting 1224. thelmores:
Once again in awe of genesis...... believe we could have a brief window where this storm could get classified..... again!


you gotta be kiddin me...
does anybody know when conditions are supposed to start getting favorable for development?
(generally speaking, not regarding 91L specifically)
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1227. Patrap
Right on thel..

A self organizing system, fractal to the core, not unlike a Galaxy, or other self organizing system.

Awe is the right word.


Member Since: July 3, 2005 Posts: 426 Comments: 128866
Quoting 1198. beell:


It's no different than the 48 hr product. It gets issued 4 times per day. To our delight sometimes, and to our consternation!

And, it is still an experimental product as far as I can tell. You can tell NOAA what you think at:

NWS Customer Survey for Official and Experimental Products/Services-Extended Tropical Weather Outlook



Thanks, Beell. I've said all I will say about it. I just found it interesting, and easily confusing, to see it actually out and being used already, and I agreed with the few here that were chatting about it.

Eventually, it'll at least become as clear as mud to any of us that pay attention and care about that sort of thing. My guess is that even now only maybe 1/2 of south Floridians have any knowledge of a storm brewing just off their coastline as we speak. Such is life. ;)
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Once again in awe of genesis...... believe we could have a brief window where this storm could get classified..... again!

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Link WV Loop
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Quoting 1141. TropicalAnalystwx13:
The GFS continues to develop a tropical cyclone in the southwestern Caribbean in a little over 10 days. It tracks across the Yucatan and intensifies to a mid-grade tropical storm before making landfall near Tampico. While this scenario is certainly plausible, and actually favored as a weak pulse of the MJO passes across the west Atlantic...and the TUTT retrogrades westward allowing for a favorable upper-air environment...we might want to be careful of the GFS' tendency to over-amplify the monsoon circulation when bringing the MJO in our neck of the woods. I'd give it a bit more credence considering the CMC and ECMWF show a lowering of atmospheric pressures across the region in the extended range.



There have been practically countless tropical systems over the past few years that have developed in the western Caribbean and crossed the Yucatan and make a second landfall in Mexico...
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1221. whitewabit (Mod)
Quoting 1213. Chicklit:
If it rains in the morning I will still go out on the golf course. I need to see some green. Been in an office all week!
please...keep 91L offshore...


love to walk the courses . people don't realize its like walking in a park with out all the people ..

Just starting to rain here .. will be short line of showers isn't very wide ..
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1220. ncstorm
that is one big spin near texas..
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Quoting 1212. AstroHurricane001:
Gulf Stream interaction, weak steering and minor-TUTT interaction will do that to a tropical disturbance.

Vancouver, BC has gone 31 days without rain.

Mild temperatures in Ontario with thunderstorms.

All of China is under a country-wide high heat alert, for the first time in history.

The Steamboat Geyser in Yellowstone National Park erupts.


Even Tibet and Manchuria?
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1218. Patrap
Indeed 1900,

One can see the Core elongate toward the Neast in the WV loop easily.

It's outta here...promptly

Member Since: July 3, 2005 Posts: 426 Comments: 128866
1216. mrmombq
Quoting 1210. FIUStormChaser:
Still can't tell if the system moved east, which it appears or a convective blowup is diverting my eyes.
entire circulation still appears stationary with the convection only moving slightly east.
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1215. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128866
1214. ncstorm
thanks both!
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If it rains in the morning I will still go out on the golf course. I need to see some green. Been in an office all week!
please...keep 91L offshore...
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Gulf Stream interaction, weak steering and minor-TUTT interaction will do that to a tropical disturbance.

Vancouver, BC has gone 31 days without rain.

Mild temperatures in Ontario with thunderstorms.

All of China is under a country-wide high heat alert, for the first time in history.

The Steamboat Geyser in Yellowstone National Park erupts.
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Quoting 1195. ncstorm:


I dont see on the surface map where a trough is evident? Is there another map I should be looking at? The front has stalled I see but I dont see a trough? I thought the front was supposed to kick it out to sea?



what a trough would look like on the WPC surface map

Not a surface trough, but a mid-upper level trough. Using both an model analysis and a water vapor loop, the trough can be seen digging south to near 91Ls location. In addition, the fast movements of the cloud tops indicates the shear the trough brings with it.



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Still can't tell if the system moved east, which it appears or a convective blowup is diverting my eyes.
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Quoting 1182. beell:


I agree, and your point is well taken on any area of disturbed weather that does not follow a simple trend of increasing organization.

I think you have to consider it as two separate products. Pretend the 48 hr product does not exist-91L has a 50% chance of becoming a tropical cyclone over the next 5 days.



You say pretend it doesn't exist and presume 50%...that could be...but if I presume 10% or 0% in day3-5 than 40/40 is still right.
.
In chatting it out, amicably and well-thought out(are you listening NHC) I might add, the bottom line might be that if the second number is day1-5 then it's useless in a declining with time storm....only of some use in the growing with time storm....and even that is subject to interpretation and confusion. Does 40/60 mean a straight-forward growing storm or does it mean a storm that if it survives the next 48hours would be then forecast to bloom?
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1208. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128866
Quoting 1200. Naga5000:
I'll try my best to explain probability over time intervals in inclusive events since we seem to have a hang up there. In this case we have two time intervals, 2 days and 5 days. Because the time intervals are inclusive (meaning one is part of the other), the 2 day probability will always be part of the 5 day probability. We should never see a 5 day probability lower than a 2 day probability. However, we can see a 5 day probability higher than a 2 day probability as the chances of an event occurring can, of course, increase over the non overlapping part of the interval. It's important to note that in probabilities over time intervals, the larger the interval, the less reliable the probability will become.

In case anyone wants to see it, here is the powerpoint on the 5 day experimental TWO. It has some neat information regarding verification of their forecasts. Link


worth bumping to the next page!
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Quoting 1195. ncstorm:


I dont see on the surface map where a trough is evident? Is there another map I should be looking at? The front has stalled I see but I dont see a trough? I thought the front was supposed to kick it out to sea?



what a trough would look like on the WPC surface map


You are correct and I am totally off the mark with the comment; fell asleep on the couch after dinner, just logged on, and am still semi-conscious.

I meant to say front, etc.......Ignore my comment below.............. :)
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Quoting 1192. moonlightcowboy:



Five days ago many of us were giving up on Dorian. From that perspective, the new forecast may have made sense, but during that time the forecast also said zero percent chance of development as well. It's going to have to get explicitly explained or it will confound and confuse the general public further.

I'm not sure I understand the purpose, as given anyways, and they need to get this clear especially since we're smack in the middle of season.



Supposedly according to the NHC, they are using it experimentally for this season.. Why start in the middle of the season? Dunno
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Good Night All! Going to be an interesting night, and Saturday , for 91L and the blog ! See you all in the AM !
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1203. Patrap
The WV latest frames show the impingement on the N and NE side from the Winds aloft, and maybe a slight nudge Ne shown in the convective burst near the coc.

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1201. mrmombq
Quoting 1190. seer2012:
It appears that the storm is situated between two opposing steering forces.At the moment it appears to be either stalled to a slight southerly movement.
agree
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I'll try my best to explain probability over time intervals in inclusive events since we seem to have a hang up there. In this case we have two time intervals, 2 days and 5 days. Because the time intervals are inclusive (meaning one is part of the other), the 2 day probability will always be part of the 5 day probability. We should never see a 5 day probability lower than a 2 day probability. However, we can see a 5 day probability higher than a 2 day probability as the chances of an event occurring can, of course, increase over the non overlapping part of the interval. It's important to note that in probabilities over time intervals, the larger the interval, the less reliable the probability will become.

In case anyone wants to see it, here is the powerpoint on the 5 day experimental TWO. It has some neat information regarding verification of their forecasts. Link
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1199. Patrap
By my best est, the system has stalled for the last 7 Hours, with a center becoming better defined the last 2.

Note the Western side of the circ..
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1198. beell
Quoting 1192. moonlightcowboy:



Five days ago many of us were giving up on Dorian. From that perspective, the new forecast may have made sense, but during that time the forecast also said zero percent chance of development as well. It's going to have to get explicitly explained or it will confound and confuse the general public further.

I'm not sure I understand the purpose, as given anyways, and they need to get this clear especially since we're smack in the middle of season.


It's no different than the 48 hr product. It gets issued 4 times per day. To our delight sometimes, and to our consternation!

And, it is still an experimental product as far as I can tell. You can tell NOAA what you think at:

NWS Customer Survey for Official and Experimental Products/Services-Extended Tropical Weather Outlook
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Quoting 1191. Patrap:


On the radar, the convection appears to be moving NE? but it appears to be moving S?
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1195. ncstorm
Quoting 1188. weathermanwannabe:
Good Evening. NHC went up to 50% over the next 48 based on the outstanding presentation this afternoon while the system was moving very slowly to the North (perhaps giving it some hope so to speak) and starting to organize. However, the trof and accompanying sheer band decided not to wait for it to move North and decided dive on down South into the circulation.......The trof won the timing battle.

Looks like it might put the final El Kabong on the remnants by tommorow morning.


I dont see on the surface map where a trough is evident? Is there another map I should be looking at? The front has stalled I see but I dont see a trough? I thought the front was supposed to kick it out to sea?



what a trough would look like on the WPC surface map
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1194. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128866
Quoting 1187. TropicalAnalystwx13:

The remnants of Dorian are not a sub-940 millibar monster. Here's the correct steering layer =P



Sorry

Quoting 1185. ncstorm:


getting a comma shape..


Yeah..

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Quoting 1182. beell:


I agree, and your point is well taken on any area of disturbed weather that does not follow a simple trend of increasing organization.

I think you have to consider it as two separate products. Pretend the 48 hr product does not exist-91L has a 50% chance of becoming a tropical cyclone over the next 5 days.






Five days ago many of us were giving up on Dorian. From that perspective, the new forecast may have made sense, but during that time the forecast also said zero percent chance of development as well. It's going to have to get explicitly explained or it will confound and confuse the general public further.

I'm not sure I understand the purpose, as given anyways, and they need to get this clear especially since we're smack in the middle of season.
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1191. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128866
It appears that the storm is situated between two opposing steering forces.At the moment it appears to be either stalled to a slight southerly movement.
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Quoting 1187. TropicalAnalystwx13:

The remnants of Dorian are not a sub-940 millibar monster. Here's the correct steering layer =P


I was just about to post that, but you beat me to it.
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Good Evening.
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Quoting 1184. FIUStormChaser:


Here is the steering...


The remnants of Dorian are not a sub-940 millibar monster. Here's the closest steering layer =P

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Is he gonna do a loop?
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1185. ncstorm
Quoting 1177. FIUStormChaser:


Is the center still stationary?


getting a comma shape..
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Quoting 1179. tornadodude:


Almost appears to be drifting south, if not slightly south east..


Here is the steering...

See post 1186. TAWX13
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Blob SE of Nova Scotia looks nice. Just pointing it out. Also 91L is getting there, much better organized than earlier.
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1182. beell
Quoting 1153. CosmicEvents:
That's the problem.
.
If it's day 1-5 and not day 3-5 then we're left guessing about what the probability is day 3-5. 40/40 could mean 40/0, 40/10, 40/20, 40/30 or 40/40, or 40/50 even if it's a close call.
.
They need to clarify the point for the prob and wx geeks.


I agree, and your point is well taken on any area of disturbed weather that does not follow a simple trend of increasing organization.

I think you have to consider it as two separate products. Pretend the 48 hr product does not exist-91L has a 50% chance of becoming a tropical cyclone over the next 5 days.



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Quoting 1167. VAbeachhurricanes:


What? this isn't hard. If there is a 50% chance to form within two days, and they don't think it'll increase after day two then the prob. stays the same. Because if it happens within two days, it also is concurrently happening in 5 days.


Right, these aren't independent events.
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Quoting 1173. sar2401:

I'm sure this sounded like a good idea at the time but, if they are just going to give the same probs for all five days, they haven't made a helpful change. This is the first storm to test the system and it certainly appears no one is willing to go out on a limb and lower the 5 day probability, which makes absolutely no sense.

Having the same formation percentage for both the 2-day and 5-day outlook simply means that conditions will be favorable in the next 48 hours as opposed to 120 hours. It wouldn't make any sense to give one percentage for the 2 day interval and then an even lower percentage for the 5 day because the former falls within the latter. If conditions are expected to become more favorable, then the 5-day will have a higher percentage than the 2-day. We see this currently in the East Pacific:

1. A SMALL LOW PRESSURE SYSTEM LOCATED ABOUT 950 MILES SOUTHWEST OF THE
SOUTHERN TIP OF THE BAJA CALIFORNIA PENINSULA IS PRODUCING
DISORGANIZED SHOWERS AND THUNDERSTORMS. WHILE ENVIRONMENTAL
CONDITIONS ARE NOT CURRENTLY CONDUCIVE FOR DEVELOPMENT...THEY
COULD BECOME MORE CONDUCIVE DURING THE NEXT SEVERAL DAYS...

PARTICULARLY IF TROPICAL STORM GIL CONTINUES TO WEAKEN. THIS
SYSTEM HAS A MEDIUM CHANCE...30 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS...AND A MEDIUM CHANCE...40 PERCENT
OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS...AS IT MOVES
WESTWARD AT ABOUT 10 TO 15 MPH.

...I think.
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Quoting 1177. FIUStormChaser:


Is the center still stationary?


Almost appears to be drifting south, if not slightly south east..
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1178. sar2401
Quoting VAbeachhurricanes:


What? this isn't hard. If there is a 50% chance to form within two days, and they don't think it'll increase after day two then the prob. stays the same. Because if it happens within two days, it also is concurrently happening in 5 days.

Yes, it is that hard. You're saying that if there's a 50% chance a storm will form in two days and it doesn't, that mean the probability of it not getting high or lower than 50% in the next three days is zero? If so, get rid of the two day and just make it five days. 91L is a prime example. Do you actually think, if it doesn't improve in the next two days, the probability it will improve in the next three days is not going down? This is simply needless confusion with no added information.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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