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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well they also found pressures lower than the 1004 they sampled
TS BUSTED FORECAST ALIBI
T.C.F.A.
XXL/XX/INV97
MARK
14.77N/55.21W
ALERT ATCF MIL 97X XXX 110820060000
2011082006
14.0 307.0
14.5 298.0
100
14.3 307.0
200600
1108200600
1
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
WTNT21 KNGU 200600
RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE
WITHIN 100 NM EITHER SIDE OF A LINE FROM 14.0N 53.0W TO 14.5N 62.0W
WITHIN THE NEXT 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF
A NUMBERED TROPICAL CYCLONE WARNING AT THIS TIME. WINDS ASSOCIATED
WITH THIS DISTURBANCE ARE ESTIMATED TO BE 25 TO 30 KNOTS. SATELLITE
IMAGERY AT 200300Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 13.9N 051.8W AND IS MOVING WESTWARD AT 08 KNOTS.
2. REMARKS: THE DISTURBANCE IS EMBEDDED WITHIN THE CYCLONIC FLOW OF
AN UPPER LEVEL LOW NEAR THE LESSER ANTILLES LOCATED AT 14.0N 053.0W,
WHICH IS PRODUCING 20 TO 30 KNOTS OF NORTHWEST SHEAR OF THE SYSTEM.
THOUGH DRY AIR IS SUPPRESSING DEVELOPMENT AT THIS TIME, AVAILABLE
SATELLITE DATA DEPICTS SLIGHT ORGANIZATION ASSOCIATED WITH THIS
FEATURE. CURRENT MODEL GUIDANCE DEPICTS INTENSIFICATION OF THIS
DISTURBANCE AS ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BECOME MORE
CONDUCIVE FOR DEVELOPMENT OF A TROPICAL DEPRESSION OVER THE NEXT 24
HOURS. SEA SURFACE TEMPERATURES ARE CURRENTLY RANGING FROM 84 TO 90
DEGREES FAHRENHEIT.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED
BY 210600Z.//9711081712 127N 335W 25
9711081718 129N 344W 25
9711081800 130N 356W 25
9711081806 131N 370W 25
9711081812 132N 392W 25
9711081818 132N 413W 25
9711081900 133N 435W 25
9711081906 134N 455W 25
9711081912 135N 474W 25
9711081918 137N 493W 25
9711082000 140N 512W 25
9711082006 143N 530W 30
Pfffff
BOOM + TRACK = DOOM
The dropsonde that was based on missed the eye:
1004mb (Surface) 230° (from the SW) 38 knots (44 mph
So actual would be 2-4 mb lower.
So very true! Our last was Wilma and although people remember things about not having power for weeks or gas, etc. not much else...and you do become complacent when threats are not "regular" so to speak. I have neighbors that have not prepared at all because of that.
15 N is mid way the island chain, fairly low for an easterly wave. Current steering is very zonal and to the West to a point South of PR and then WNW all he way from there to the GOM. That is also the long range steering forecast out to Wed. next week.
It will have a tendency to track just N of due West but not by much over the next 24 to 48 hours based upon what I see as the set up out there now. Current heading looks like 275 degrees
97L's recon fix is scheduled for 20/1800Z, which is about 1 PM eastern time.
I would go with Elevated.
would a weaker storm go futher east or west based on steering patterns?
LMAO....Guarded
No problem. Lots of time to watch this one.
on harvey
West
Irene has a legacy to come up too, in 1971, 1981, 1999, and 2005 Irene became a hurricane.
Lots to watch for over the weekend
A landfall about halfway between MullinsRiver and BelizeCity puts it in HurricaneAlex(2010)territory. And Alex started its Yucatan-crossing as a TropicalStorm
Kenny~ I'm somewhere between low & guarded (torn between putting some Kahlua in my coffee or a nap). If I was out on the islands I might be up higher with ya.
Yep, without a deep low it doesn't get pushed around by upper-level steering currents as readily.
ASCAT on fnmoc
does not indicate one, pass was little over an hour ago.
Caution: .mil website, you will get a security warning
A very good update Bob!
LOL, do you have crow handy? you will be eating it in about 24hrs.
FINAL APPROACH
What's HWRF showing?
lol...
very much enjoyed your penalty box post.
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