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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The GFS shows 6-hour accumulated precipitation, so keep in mind that for a westward-moving storm, especially one as fast as 97L is moving, the precipitation will appear to be weighted to the east of the storm. In reality, instantaneous precipitation rates are shifted a bit more west.
Based off this image, the surface circulation (look at the wind barbs) is very far removed from the mid level circulation (cloud tops), indicating a very disorganized system. Now two options exist. Either a, it could try to form another surface circulation under the mid level circulation, or b, it will try to eventually align the mid and low level circulations. Either way, both of these solutions will not come by quickly and will hamper development over the next few days.
Personally, I'm surprised by the NHC's decision to put it at 60%.
111 hours out a little farther north then 18z gfs
Your welcome, I thought it was interesting.
Meteorology, computers, automated scripts/code, fraka-fraka daylight savings, etc.
Hi aquak.
So I'm assuming that you're making dessert tonight? What do you have in mind?
WV
The Tampa episode of "It Could Happen Tomorrow" paints a pretty clear picture of what would happen to Tampa should a Cat 3 strike just north of the city. As beautiful as Tampa Bay is, it would become the ugliest thing on Earth in this scenario.
Man, and you cross reference with past runs. I'm a notary, lets get this deal done. I seen it, that's all we need to make it official :-b
If 97L can stay on the GFS's current track for 0Z the interaction with the mountainous terrain of Hispaniola will be limited!! Although it could be close enough to limit convection, especially on the northern side of circulation!!JMO
best dessert will be when dfw posts the last frame of the run and this mess totally dissipates- like I said, in my dreams
123 hours out
I have never seen one in the last 10 years now we have tons. They are called cicada killers.
Yes. It is. I've got a bunch of links about her somewhere I'll try to find them and send them your way. :)
Checking in quickly so i see we have Harvey for Belize and Honduras to deal with, and 97L is organizing into a pretty nice invest as well and could be named a TD as early as Sunday. 98L seems to be dealing with some dry air in the upcoming days, and will likely not be much for a while, but it does show you we are nearing that time of the Season where we have to watch very closely for Cape Verde Developments, though i dont have a clue why they initiated another invest to the SW of 98L just becuase there's two seperate Lows(Monsoonal & Tropical Wave Low) either way, 99L should'nt come to much and if anything could prohibit development of 98L and keep it a little less organized until they detatch and 99L stays in the ITCZ and 98L heads off to the NW/WNW... Anyhow i see Harvey could also be our first Hurricane of the season according to the Latest advisory by the NHC, it's strengthening pretty nicely from a 40 Mph storm this morning to a 60 mph storm tonight, and in my opinion will end up peaking jsut short of the mark at 70 Mph... though wouldn't be surprised to see a hurricane.
Anyway thats my take on today, will be back here tomorrow...
Nice work.
135 hours out
I know that zone; I used to inhabit it myself...I think my room is still waiting on me...LOL
I have them out of nowhere, too. We call them ground hornets.. ours that look like that build underground.
Cicada larvae/pupae have a 17-yr life cycle. Must be a big outbreak of them coming.
The break is still there for the system to move toward in the weakness.....not much doubt if this model is correct where it is going.
Bombing out. we shall see what happens next few frames.
Rhut Rho. GFS is following the ECMWF now.
Who doth dare to dispute the word of he who did appoint the designated poster, Sir (or Madam) dfwstormwatch. Let it be known to all men and women, that at all times, time shall be presented in Greenwich Mean time. So state this day .. . blah blah and so on.
I for one am glad we have Sir (or Madam) dfwstormwatch at the watch, because I really have to get some sleep.
NEVER MIND THAT @?#!, HERE COMES MONGO HOUR 144
It's like waiting for a telegraph message...in Internet times. Very cool.
144 hours out
Looks like Fay 2.0
JFV will be happy.
Well if the NHC says theres a possibility of Harvey attaining hurricane status, I'm with them.
Floods,droughts, tornadoes,tropical storms, now locusts?
Houston, we got a problem.
you're not! we are all enjoying the play-by-play. Please, proceed.
ok, not "enjoying", so to speak...actually my poor tummy is hurting.
On such a track, convection would be abundant along the north-facing slopes of Hispaniola's mountains, providing them with heavy rains that they don't need. Dried-out inflow due to downsloping on the other side of the mountains would then try to choke the northern side of the core of the cyclone.
156 hours out and ahead of the competitors
Only saying that it *could* cross that cat 1 threshold.
But:
The biggest hindrance might be dry air, but if it ceases ingesting mid-level dry air (as any mature TC should), that will not stop it either.
loks to me like it goes over central cuba, does not have very many high mountains I think
LOL!
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