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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you still working. But I'm not sure what's happening, it's definitely got some issues right now
I like your attitude :-)
LOL... hey yester... some of it is some old cusses trying to sound like young cusses... some of it is young cusses using slang... and some of it is just pple joking other people... lol
Thanx for the nice animation GeoffreyWPB...
Good morning to you!
This is what my mother in law would have politely referred to as being "Snake Bit."
.FIRE...
ELEVATED FIRE WEATHER CONDITIONS EXPECTED TO PREVAIL INTO EARLY NEXT
WEEK. THE ISO TSRA CHANCES THE PAST COUPLE OF DAYS TO DECREASE A BIT
AS WE ARE NOT SEEING A LOT OF SHORTWAVE ACTIVITY HEADING THIS WAY IN
THE UPSTREAM FLOW. OTHERWISE THE MAIN ISSUES REMAIN THE AFTERNOON RH
VALUES WHICH ARE EXPECTED TO MIX OUT INTO THE 23-35 PERCENT RANGE IN
THE AFTN. HOWEVER WINDS SHOULD REMAIN ON THE LOW SIDE. VERY LIGHT W/
SWLY WINDS IN THE MORNING TO SHIFT TO THE SOUTH AND INCREASE TO NEAR
10 MPH DURING THE AFTN WITH THE PASSAGE OF THE SEABREEZE. LOOKING A-
HEAD...MODELS TAKING A POTENT TROPICAL SYSTEM INTO FL BY THE WEEKEND
OF THE 25TH. THIS PATTERN SHOULD SHIFT WINDS TO A MORE NORTHERLY DI-
RECTION ACROSS SE TX AND THE PROXIMITY OF THE CIRCULATION ASSOCIATED
WITH THE TROPICAL SYSTEM MAY BRING WINDS CLOSER TO 15 MPH BEFORE ALL
IS SAID AND DONE. STAY TUNED. 41
Case in point :-)
DVORAK Estimates rising again.
Easy there, we're not all as dumb as we look...
By the way....I understand your comment and you are in someways correct. But let me say something kinda funny. There is ALOT of pin the tale on the donkey that goes on at the TPC. I have been there and personally witnessed it many times at the TPC while visiting. As a matter of fact, "lets flip a coin" is not a rare comment there. The truth is a HUGE HUGE amount of weight is placed on models and consensus, significantly reducing the role of individual forecasting as years have gone by. The role of the forecaster is much greater in the very very near term track. So the guessing game on here is not far off than that at the hurricane center...so long as its in reasonable contrast to the models. Thats not to say they are never wrong, they are. But so are many many forecasts by some very intelligent people.
Yeah. Looks that way to me too. :)
06z GFS
Looking at that diagram from SFWMD.. I did notice one thing I thought was interesting..
BAMS has it S. of central Cuba then cuts it dearly due N. compared to the BAMM and BAMD.
Some shear between the low and mids at that point perhaps?
Seen that with a couple of the BAM suite runs.
what does it have as a pressure there? 996mb? Or did I see the first outer ring?
Still a long way off... intensity progs are for entertainment purposes only at this point... but still is interesting.
Wow, up early to bring value to this blog. Nice.
Yes, West Palm Area and I am beginning to get VERY interested in this system!
I thought she was referencing the trolls... lol
Anyway, 6z GFS time since I have waited up to post my take on it at my 'home', but please anyone in the Eastern Gomex and to the Bahamas keep an eye out, and listen to the many well informed bloggers you are lucky to have here, they can give you great insight into what is likely to unfold.
Euro 168.....
GFS 144...
Hurricanes and tropical forecasting when it comes to TV is not fun. While of course you want to get the word out about the potential impacts of an impending system, you also don't want to create a sense of panic. A hurricane can make or break a TV station, so a lot of TV mets like myself have to take the high road on these scenarios until we are fairly certain of some kind of impact. It doesn't mean that we don't want to get information to the public about what could happen next week, we've been preparing our viewers for this since mid-May.
I'm in that club folks... in Boca Raton... so I've been watching for a week now... starting to look like an interesting week possibly.
Yep, I am already making preliminary plans for my prep next week, should it become necessary. Always good to be ahead of the curve.
I've done a cursory look for this in a couple of places... but is there a quick reference for translating mb to inches... or maybe a formula?
Oh wow. Glad we have a fresh, well rested brain here this morning. I been up all night and forgot the 6z Run. Of course I seem to forget a lot of things lately. Hmmm?
Lol. Thanks MH9! :)
Yeah. Waiting on visible.
To convert millibars to inches of mercury, multiply the millibar value by 0.0295301.
Or just bookmark this.
LOL, not really restarted, just slept 45 minutes, but just enough to keep me going until at least 8a.m lol.
Got to sleep early yesterday so missed the 00Z and 06Z runs but got caught up just now. All I can say is wow...
Do you ever sleep? You're always here - LOL! I usually just lurk when it's really busy on here, no need to repeat all the stuff that gets posted.
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