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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Yeah, that's a good point.
lol.
Ahhhhh....with all due respect, there is no way you can say that NO ONE on here is a psychic.
I knew you were going to say that!
What will the winds beon harvey at 11??
a 45
b 50
c 55
d 60
e more than that
What will harveys winds be at landfall??
a 50
b 55
c 60
d 65
e 70
f greater than that
when will 97 be named???
a never
b 1-2
c 3-4
d after
when will 98l be named??
a never
b 1-2
c 3-4
d after
when will 99l be named???
a never
b 1-2 days
c 3-4 days
d after
Stop asking if 97L is going to affect your city. It's in the central Atlantic. No one knows where EXACTLY it will strike. No one here is a psychic. Just follow along.
+1
Can't remember, though I have fished down in south central VA, in Nottoway County, Ft Pickett.
Ah, I think we all decided the "psychic twins" are indeed, well, psychic.
I think they got a little too excited over the mid-level circulation, when the surface winds flowing underneath of it have been all out of the northeast. They are also very confident due to the model support, but they might be pushing the 48-hour window a little bit. We'll see.
not likely at all
The models usually flip flop back and forth. Just pay attention and stay informed. NO ONE KNOWS where this thing could go if it truly does develop. THe models might have it hitting Mexico next ...lol..just stay tuned.
ROFL at TF!
couldnt we very easily see a low level circulation form under the well defined MLC?
CDBDA
C
E
B
C
E
Well we aren't in any kind of drought, maybe 1" below normal, but that can easily be made up by our thunderstorms that have been rolling through.
The question is whether we sit around waiting for them to straight out, or whether we straighten out first. It is no good to rely on waiting for model consensus. What we are truly waiting for is 97L to develop a center. Once that happens, we will have a much better grasp on which path it might take. Until then, we are playing games guessing where it will enter the Caribbean. The system is so large that it could be anywhere from St. Lucia to Guadelope, depending on where the center forms.
Hurricane
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 20 AUG 2011 Time : 011500 UTC
Lat : 16:35:59 N Lon : 85:20:40 W
CI# /Pressure/ Vmax
3.5 / 993.0mb/ 55.0kt
Final T# Adj T# Raw T#
3.0 3.5 3.9
raw t's going up again
how about now
That is true!! What i gather from all this eery model consensus is that we should be prepared as the models are picking up on ripe conditions with the MJO returning, the TCHP being very favorable, and steamy GOMEX temps.THis all points to tropical troubles in the making. Exact track will work itself out eventually, although i really don't think the CONUS can avoid effects from 97L should it develop!! I'm not DOOMCASTING either!!!
this blog cannot be good for a heart patient! My guess ....if you are in the path today means you wont be there tomorrow!
And y'all wunder why I'm so adamant about differentiating between North and South Carolina...
Even weakening strong tropical storm?
That's what we're waiting to find out. Such a large system could spin up a surface vortex anywhere with in a fairly large region. It should be near the NW end of the tropical wave, but that still leaves a lot of latitude (literally) for it to pick from.
That's some solid convection right there... if it sustains itself and continues to organize further, RI is indeed a possibility given it's small nature.
big clouds
Wrongo!!! I make reservations at least a week out as I have animals to travel with, plus it takes me several days to prep my house. I watch every minute VERY carefully!
WOAH!! Firing some really cold cloud tops.
WOW!
No.
nop not tonight
1. What is a troll, i see everybody writing Trolls?
2. What is DMAX?
No, thats too early
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