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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This is an Igor/Julia type situation. They were very close to each other. If 98L develops, it will move out to sea. 99L will take the more westerly track.
or "the chart" !!
Ok so effects is a wide term.
And "the storm" 97L is modeled to possible large dimensions.
Like Wilma coming in on Fl West coast.
Got it thanks.
97L be comes the I storm
98L be comes the J storm
99L be come the K storm
that would put us at 4 more storms on top on the storms we this had
That was what I was thinking
99L would probably be more likely to develop than 98L...98L is headed toward cooler waters in a couple days.
I don't see it there.
Center of cyclonic turning appears to be at 11.2, 48W
FULL
And check what's coming behind....
To take advantage of Moist Air, Low SAL, Everything Good for TS development.
What are the Hinderances next 4-5 days???
What is Shear forecast ?
Gosh, you are missing a lot of stuff that we have fun with on the blog!
Somebody fill this poor fellow in!
That's where I see it too.
Strange Vorticity Signature
Kind of depends on the track they both take. I could see 99L heading out to the WSW or directly W because of how far South it is and 98L heading off to the NW due to how far North it already is. If they do this and separate some then both could develop, right now 99L looks to be in better shape to develop. By early next week this could get fun! Sure glad most of the kids will be back in school!
97L becomes the "I" storm
98L becomes the "K" storm
99L becomes the "J" storm
That is what I think is going to happen. LOL besides only a "Jose" can cruise through the Caribbean and feel right at home.
If 97L can avoid 'mountainous Hispaniola' and stay to the north and maintain its strength, a track towards the eastern side of the guidance would be more likely. If it is weakened over 'mountainous Hispaniola' or heads to the south, a track afterwards on the western side of guidance will be more likely I think.
If a center forms north of 15N now that could be critical, or the convection building south and creating a true center down near 14 N would be critical also. Or splitting the difference?
Wind direction???
If there is actually a closed center of any kind, it's way down near 11N, 48W. However, the nature of this negatively-tilted tropical wave means that tropical development will likely occur on the northwestern end where the convection currently is. If we make that assumption, then we are basically dealing with an open wave without a closed circulation.
Yes that is true. I was saying it will probably be "Jose" because it's organization in thunderstorm activity is far greater than 98L
and with this...400 posts full of blithering, unfocused hysteria has been distilled into an easily understandable thought...
HWRF almost made it look like 97L had a mind of its own to know how to minimize land interaction.
I'm now more inclined to agree with you on this. I initially thought it was around 14N, but if you look carefully you can see the lower level clouds rotating around a mean center in that area. I assume the low is still broad? a href="" target="_blank">
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