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
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19/1745 UTC 13.2N 49.0W TOO WEAK 97L
Watching it this evening should be fun. As it's passing 50W, we'll see what kind of dress rehearsal 97L puts on.
97L is looking good.
Lol yup my house would have been ripped as well.
97L looks good to me on satellite, very large system with just a little bit of dry air that is still inhibiting further development.
Link
SYNOPSIS FOR CARIBBEAN SEA AND TROPICAL N ATLC FROM 07N TO 22N
BETWEEN 55W AND 65W
530 PM EDT FRI AUG 19 2011
.SYNOPSIS...NEWLY UPGRADED TROPICAL STORM HARVEY IS CENTERED
NEAR 16.5N 84.7W 1002 MB AT 5 PM EDT MOVING W OR 280 DEG AT 10
KT. MAXIMUM SUSTAINED WINDS ARE 40 KT WITH GUSTS TO 50 KT.
HARVEY IS FORECAST TO BE NEAR 16.7N 86.1W AT 2 AM SAT...REACH
NEAR 17.1N 87.9W AT 2 PM SAT...AND INLAND NEAR 17.6N 89.9W AT 2
AM SUN.
LOW PRES IS DEVELOPING ALONG A TROPICAL WAVE NEAR
13.5N47W. THE LOW...POSSIBLY A TROPICAL CYCLONE...WILL REACH
NEAR 14N52W EARLY SAT...NEAR 15N55W SAT AFTERNOON...NEAR 16N60W
EARLY SUN...NEAR 16.5N62W SUN AFTERNOON...AND NEAR PUERTO RICO
SUNRISE MON.
http://www.nhc.noaa.gov/mobile/MIAOFFNT3.html
08L/TS/H/CX
NEARING LANDFALL
A little wind, a little rain. Just what the doctor ordered!
Check to make sure you're still logged in.
shes pushing that dry air around her to the south, if it doesn't come in between her and the inner core look out. keeping a watch on this one
I think it is a little too early to add Nearing Landfall, when it is over a day away.
INV/XX/97L
MARK
13.51N/49.88W
Yes and zonal shear looks favorable for it in the carrib assuming it goes there.
Joe Bastardi
Western gulf threat period not till after Sep 1. Irene to be is my fla threat storm( near 15 north, 50 west)
Very impressive banding and firing some really cold cloud tops.
BBL
No way to say, but if I were you I would definitely be doing some storm prep, just in case. Looks like it could be fairly close, but then again, that's almost 3 days out.
here's the pic again, for everyone who didn't see
Time to upgrade the DOOM:COM forecast!
wonder what makes him say that...
I think there is a good chance that it starts rapid intensification soon, if it hasn't already.
Very much improved since this morning.
Texas has it's shield up.
Twitter him. Maybe he'll answer.
Impressive considering we were approaching DMIN...
XX/INV/98L
I agree.
The diurnal cycles do not have much affect on tropical cyclones, that is mainly for tropical waves and such.
yeah, it has been up forever it seems. I mean what makes him think it will change after Sept.1st?
Now:
Much better organized today...banding features starting to become evident. Shear is a little less today and the mid level environment is slowly moistening. Appears as if we will see development into TD 9 by this time tomorrow if this trend continues.
My talking point right now is how much land interaction there will be once this system rolls through the Caribbean/just N of it.
with a high over the rockies, a high over bermuda, and a trough of low pressure in the northern great lakes region which the models are depicting it favors a florida hit.
Well I mean that set up has to change eventually (I mean theoretically it does) Maybe the models are hinting at that in the longer range.
Viewing: 1401 - 1451
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