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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Tropical Cyclone Advisory #17
TROPICAL DEPRESSION, FORMER FERNANDA (EP062011)
11:00 AM HST August 19 2011
=====================================
SUBJECT: FERNANDA Weakens Into A Tropical Depression
At 18:00 PM UTC, Tropical Depression, Former Fernanda (1005 hPa) located at 15.4N 145.8W or 610 NM east southeast of South Point, Hawaii has sustained winds of 30 knots with gusts of 40 knots. The cyclone is reported as moving west at 10 knots
Dvorak Intensity: T2.0
Forecast and Intensity
======================
24 HRS: 16.0N 149.3W - 25 knots (Tropical Depression)
Agreed.
If it was not for the pool of dry air to the west and south of 97L, it would be a Tropical Storm already I think.
And I was kidding about the Doom part.
Shucks!
:):))
And your basing off all your opinions from last year, every year is different, you can't just say nothing will hit the US this year, that'll make people think they're safe when they really are vulnerable.
He never said nothing was going to develop.
I disagree. The MJO is increasing our odds at seeing more convergence and storms across the Atlantic. Waters are warmer, and the overall weather pattern is shifting to a US impact.
You have to think about this season....
Half the systems were duds that formed off old frontal boundaries. They didn't have time to develop and the overall pattern wasn't conducive for decent development. Now, we are looking at ACTUAL tropical waves coming off of Africa. NOW the season truly begins. Remember, Harvey was a tropical wave that came off of Africa. He could very well ramp up into a strong tropical storm or minimal category 1 hurricane.
HMMMMMM.... The ensemble model is always going to looks a lot different
COOL!!
A peninsula in Green Glasses....
That must mean SOMETHING !
I agree, 97L is looking really healthy.
Just thinking out loud here...
Right off the bat, the worrisome factor about 97L that indicates a ton of potential to me is it's immense circulation envelope - I'd offer a rough estimate over past few days of it covering nearly 15 degrees lat / long, almost a 1000 miles across either way... It's sheer size would hint at slow, steady pace of development to rein in a well-defined LLC - might be another couple days to get it together to declare a TD / TS... Along with usual dry air issues, it was accompanied by surge of upper level easterlies that have limited it's convection - and note how little has been generated on it's E flank... However, upper level winds are becoming more conducive for anti-cyclone development.
Couple other things (I know others prolly have touched on), I'd think it's large envelope would help offset too much degeneration with land interaction... with easier recovery back over water (wherever that happens), as every model run shows 97L deepening atmospherically almost irregardless of it's location by late next week - really ugly scenario by all accounts if draws off the 88-90 plus degree GOM waters - but again, all remains to be seen... Such a large system has a lot of westward momentum going for it, i.e., getting into at least the E GOM would seem a reasonable possibility much as the GFS / ECMWF have modelled...
Meanwhile, the present threat, TS Harvey is looking better organized by the hour... Might possibly become a hurricane but certainly appears an intensifying strong TS by landfall... LOL, any one of the previous TS' would envy it's mid level structure!
G'day!
But the dry/subsiding air is still there and it will suppress development whether the waves originate off Africa or not.
TROLL SPRAY---CHECK
SHOWER CURTAIN------CHECK
COFFEE-------CHECK
AND I HAVE ALL FLAVORS OF CREAMER FOR THOSE WHO WOULD LIKE SOME.
COFFE CAKES AND SNACKS--------CHECK
On a serious note the tropics are looking like Christmas out there.
E Coast CONUS TROF & High locations
says 50 MPH winds on Dvorak technique
1km Geo
Link
Schools are starting up again so that activity should slow down a little over the next two weeks (unless they have laptops and wifi in the classroom)........:)
I hope you bought extra troll spray cause we are gonna need it especially as we head into the peak of the season.
That is not a good thing, you want waves to develop ASAP if you don't want them hitting the USA. This happened in 2005, do you think 2005 was chalked full of Cape Verde hurricanes? No, it wasn't. There was only one, Irene. All the other waves croaked until they reached 55W and then they started blowing up. And UNLIKE Emily, and Don - all the models are still latched onto 93L, and we have to have a hurricane sooner or later. So please, stop comparing this to Emily and Don, the situations are totally different.
would you feel warm and fuzzy if you lived in estero?
Learn to see them before we're too old
Don't just take me for tryin' to be heavy
Understand, it's time to get ready for the storm
Rain or shine, it's always here to stay
All these years you and I've spent together
All this, we just couldn't stand the weather"
97L will not be a fish storm
Levi addressed that nicely awhile ago...
Yikes!!!!!!!
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