TD 8 forms; 97L a potential threat to the Caribbean and U.S.
Tropical Depression Eight formed last night near the coast of Honduras, and is headed westwards towards a landfall in Belize on Saturday. TD 8 is a small storm, so will impact a relatively small area of northern Honduras, northern Guatemala, all of Belize, and southern portions of Mexico's Yucatan Peninsula. TD 8 has just enough room between its center and the coast of Honduras to intensify into a moderate strength tropical storm with 50 - 60 mph winds before landfall. It is very unlikely TD8 has the time or room to intensify into a hurricane; NHC gave the storm just a 7% chance of making it to hurricane strength in their 11am EDT wind probability forecast. Should TD8 make it to tropical storm strength, it would be called Harvey.
Figure 1. Morning satellite image of TD 8.
Invest 97L likely to become a tropical storm next week, could threaten the U.S.
A tropical wave near 14°N 48°W, about 800 miles east of the Lesser Antilles Islands, is moving westward near 20 mph. This wave, designated Invest 97L by NHC yesterday, has seen a marked increase in its heavy thunderstorm activity this morning, but dry air to the north and west is slowing development. An impressive amount of large-scale spin is obvious in visible satellite loops, but the storm is at least a day away from forming a well-defined surface circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm, and wind shear is low, 5 - 10 knots.
Figure 2. Morning satellite image of the tropical wave 97L.
The computer models have shown an unusual amount of agreement in developing 97L over the past few days, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.
As seen in Figure 3, there has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties.
Figure 3. Vertical instability of the atmosphere during 2011 in the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Observed vertical instability (blue line) has been much lower than the climatological average from previous years (black line), due to an unusual amount of dry air in the atmosphere, inhibiting tropical storm development this year. Image credit: NOAA/CIRA.
Encounters with land will be another potential major problem for 97L. Most of the computer models take 97L near or over Puerto Rico Sunday night, then very close to or over mountainous Hispaniola Monday night through Tuesday. It is unlikely that 97L will be stronger than a 55 mph tropical storm when it encounters these islands, and passage over the islands could severely disrupt the storm. However, if 97L takes a path just south or north of Hispaniola, the potential exists for the storm to intensify into a hurricane.
There will be moderate wind shear of 10 - 20 knots to the north of the islands early next week, so a path just to the south of the Dominican Republic and Haiti would be more likely to let 97L intensify into a hurricane. A west-northwest motion is likely for 97L through Wednesday, which would bring the storm to the vicinity of Jamaica-Central Cuba-the Central Bahamas on Wednesday. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. The best model for predicting the timing and strength of such troughs over the past two years has been the ECMWF (European Center model), and this model currently brings 97L into the Florida Keys on Thursday night next week. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models.
Remember that a 7-day forecast by even our best model will be off by an average of over 700 miles, so it is too early to tell what part of the U.S. might be most at risk from a strike by 97L. This weekend would be a good time to go over your hurricane preparedness.
Figure 4. Morning satellite image of Invest 98L off the coast of Africa.
Invest 98L near the coast of Africa
A tropical wave near the coast of Africa, a few hundred miles southeast of the Cape Verde Islands, is moving west to west-northwestward at 10 - 15 mph. This wave, designated Invest 98L by NHC yesterday, is large and well-organized, with a modest amount of spin and heavy thunderstorm activity. 98L will bring strong, gusty winds and heavy rains to the Cape Verde Islands today and Saturday as the storm skirts to the south. So far this morning, top sustained winds measured in the islands were 24 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today. NHC gave the storm a 50% chance of developing into a tropical depression in their 8am advisory. Once 98L passes to the west of the Cape Verde Islands, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, but it is too early to be confident of this.
Jeff Masters
Reader Comments
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Did it really stay hurricane strength that far inland? Jackson, MS got sustained hurricane force winds? Maybe not considering they were on the west side. But places directly east of Jackson, MS? Just curious.
I think I will have one very disappointed grandson, his pirate-themed bithday party is Saturday afternoon - outside, along with 12 other five-year old pirates. Not the best time of year to try and plan a birthday party!
I said the other day..........this is a Charley like storm all over it.......
I would certainly not rule out it missing the ConUS completely yet with a sharp hook.
It stays off shore with that model.....
Strength is the hardest to forecast with a system like this that is supposed to interact with land. Although in my blog a few days ago, I mentioned I expected development by Saturday, most models were looking at Sunday thru Tuesds. When these systems interact with any land they can be disrupted. However, I have seen many storms cross over Puerto Rico and Hispaniola and regenerate into strong systems. The GFS is hinting at CAt 2 or higher, as well as some other models. I honestly do not know. I will post some intensity graphs, if you like.
I'm not saying it's going in across the top of the islands; I'm just saying that's a distinct possibility. If that doesn't happen? Ay, pobrecitos...
While your waiting i have a new one
I don't remember if it was hurricane strength for sure, but I think it was. I had friends outside Jackson who were hit and they had some bad damage done. They weren't prepared, never expected to be hit with the winds that came. It tore off the roof of their kennel, took down huge trees, etc..
Looks like Charley #2
Yet, NO was fine through Katrina, until the levees failed.
It was the MS Gulf Coast that got way laid by Katrina.
And then it was calm...very calm.
Exactly, Gulfport and Biloxi are barely mentioned or remembered and yet were close to being wiped away.
Well, this is not an intensity model, but the latest GFS. From reading your posts, you probably would be able to deduce a Category by the estimated pressure, better than I.
Here is the lastes intensity chart I could find:
thatll change 97 way north of the forecast points
where is Florida on that map? I do not see it. What have you done with our lovely state?
(Isn't it kind of unusual to have such tightly clustered models this far out, with a storm that hasn't even developed yet?)
I thought the same thing about Charlie.
I think I'll hold of on buying the Venice Beach home just for another two weeks!
I'm not kidding. I was going over there next week to look at a home for sale....
Thank you. I am not feeling well enough to do one today, though. I will post the models and my opinion during the day, though. If there is anything you would like to see, I shall try and find it for you. I am very rarely wrong on these systems, as you know from my blogs. j/k :)
There is a weekness in that area and if its a hurricane it will probably be more east and i shouldve said hug the coast but thats what i meant
Wait one more week and then go see if the home is still there.
Here is a video of the events.
Anytime, scott. What is your opinion of 97L right now? Don't worry, I will come to your defense if you are wrong later on. :)
very unusual to be this tight 5-6 days out.
Get it now and put a whole buncha insurance on it before this thing gets named.
actually the pressures in the center on many models are too high for the storm they are showing, because they cannot handle the idea of a system with that low of a pressure
except the GFDL and HWRF of course, who can show sub 900 storms at times, the rest of the models rarely if at all show anything lower than 975
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