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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LOL!
The concern is that the model does actually see those mountains, to a certain extent, and to see it strengthen the storm regardless (the even higher resolution ECMWF does also), may speak to how favorable the environment may be for intensification at that point, which means that even a short time over water after dealing with Hispaniola and/or Cuba could result in a still potent storm. We will see. Step 1 is to get it named.
Your the only one who is officially notarized so keep em coming.
Read Shakespeare much?
168 hours out Jacksonville hit and run!
Oh Lord...here in Middle Tennessee, they came out in full force during May and June of this year. They were every freaking where, and you had to be careful where you'd step or you'd get them all over your shoes. And they were so LOUD too! Thank goodness they're all gone now, and we won't have to see their big ugly red eyes again for another 13 years (we have one of the 13-year broods).
Thanks, I'd appreciate it.
How does that work? The stronger the storm, the more air it ingests from the environment. If the environment is dry, then a mature hurricane ingests more than ever (remember Typhoon Muifa recently?)
Harvey's momentary jump for joy also leaves him open to suck in a quick burst of dry air that chokes him up for a while, a problem that small systems often have when they try to intensify.
The United States.
I did a couple hours ago.
EEEEKK!! ok there I said it, EEEEK!!! you just HAD to bring Jax into the picture, didn't you?? EEEEKKK!!
(falls out into dead faint)
177 hours out Savannah hit and run this storm is a criminal!!!!!!!!!!!!
In-up-out.
And, yes, right now Harvey still vulnerable to mid-level dry air.
Levi what do you think about the GFS's solution of 98L and 99L moving it directly northeast toward the Bermuda High!! I just don't buy that and feel a more westward track would be probable!! Is there something im missing here? I see no ULL in the GFS solution to tug it northward!!!
Are FL mets talking about 97 enough? Now's the time to start awareness, not three days from now.
...At least support your own theory with correct terminology :P
I think you're thinking about the eye...which does trap air inside itself above a certain level. However, the storm very much does ingest air from the mid-level environment all the time. Why do you think the winds even exist at 700-500mb?
189 hours out system is hitting lost of major cities...
I have heard them bring 97 up in every broadcast for the last 36 hours. We have pretty good mets here. IMO
I would tend to argue that anything ingested in the lower levels will work its way to all levels eventually as the TC ventilates to the atmosphere!! Like you said In-up-out!!! Even with your solution of in-up-out dry air is still affecting the basic structure of the storm!!
And going toward Richmond, DC, Baltimore....
but this is 189hrs out tho, so....
Kinda reminds me of a Donna track almost
Well if you believe it then I will. If it wasn't for you I would say it would hit Florida as a tropical storm maybe even depression looking at that model.
204 hours out no way this is going to happen
Anyone?
~7 days from now would the earliest approach to FL from 97L. Serious talk about monitoring the system should begin soon. But without a developed system, it would take more faith in the models than usual.
Also, the models have been about as consistent as I think I've ever seen them at developing a system...
Yeah there is an ULL. Look 12 hours out northwest of the system. It's way up at 300mb, but apparently may take enough air out of a day to create a dent in the high that the wave will move towards.
You know I have felt like this for awhile now. I just did not want to feel lke the down WORD... lol
216 hours out
I have heard them bring 97 up in every broadcast for the last 36 hours. We have pretty good mets here. IMO
This is what you said.
228 hours out
and why is that?
Why do you say that? It could. I hope it's not the path. I want some rain across North GA. That run would prevent that.
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