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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I notice there are no canned veggies on that list... Also here we usually include canned milk [which is known as 'cream' in the Bahamas]and dry cereal.
he been ban
It's hard to pinpoint a "center" right now, as the low is still immensely broad. I have the center of broad turning still back around 49-49.5W. The convection is in the NW quadrant of the low pressure area from what I am seeing. It is moving 20mph as of the latest TWO, but I don't see it outrunning the thunderstorms. The upper-level flow over it is uniformly easterly anyway, in the same direction as the trade winds, which results in little wind shear. The entity could survive moving that fast without shearing the thunderstorms off if the upper winds are pushing the thunderstorms along with it at about the same rate.
That said, the fast forward motion does put a damper on 97L's ability to close off a more compact surface low.
Upper winds:
The Atlantic, Caribbean and the GOM are all below the climo average for vertical instability.
Wow
8 named storms and no cane yet.
Amazing.
long storeey but he was banned all i can say
As you know the weather is serious business and not for the faint-of-heart.
Perhaps a little low on the troll count but, yeah, that's about right.
Me either. If it had 12 more hours over water, I'd say it was likely. The new intense curved band forming around the center is worrisome and not what you want to see. It could be the beginnings of an eye wall. I'd put Harvey stronger than 40mph and Dvorak estimates agree with me.
Trolls got the best of him, he was permabanned and now has his own blog somewhere. He was a bit too agressive when it came to predicting landfall and strenght which gave him a large magin of error so ppl kept on trying to make him eat crow and he snapped.
I'm an amateur and long-time lurker. Is the CMC the Canadian model? Thx
Yup...Exactly what I said on the last page.
000
ABNT20 KNHC 191757
TWOAT
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI AUG 19 2011
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON
NEWLY-UPGRADED TROPICAL STORM HARVEY...LOCATED ABOUT 155 MILES
EAST OF ROATAN HONDURAS.
A LARGE TROPICAL WAVE LOCATED ABOUT 800 MILES EAST OF THE LESSER
ANTILLES CONTINUES TO SHOW SIGNS OF ORGANIZATION. ENVIRONMENTAL
CONDITIONS ARE EXPECTED TO GRADUALLY BECOME MORE CONDUCIVE FOR
DEVELOPMENT AS THE DISTURBANCE APPROACHES THE LESSER ANTILLES
SATURDAY NIGHT AND SUNDAY. THIS SYSTEM HAS A MEDIUM CHANCE...40
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS
AS IT MOVES GENERALLY WESTWARD AT 20 MPH.
A BROAD LOW PRESSURE SYSTEM IS GRADUALLY BECOMING BETTER DEFINED
ABOUT 175 MILES SOUTHEAST OF THE CAPE VERDE ISLANDS. THE LOW IS
PRODUCING A LARGE AREA OF SHOWERS AND THUNDERSTORMS...AND
UPPER-LEVEL WINDS ARE FORECAST TO REMAIN CONDUCIVE FOR SOME
DEVELOPMENT AS THE DISTURBANCE MOVES WEST-NORTHWESTWARD OR
NORTHWESTWARD AT 10 TO 15 MPH. THIS SYSTEM HAS A MEDIUM CHANCE...50
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAIN AND STRONG GUSTY
WINDS ARE POSSIBLE IN THE CAPE VERDE ISLANDS TONIGHT THROUGH
SATURDAY.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER BEVEN/STEWART/WROE
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Page last modified: Friday, 19-Aug-2011 17:57:42 UTC
Yes it is.
Harvey
If recon shows Harvey up to 45-50kt then I would say we could see a decent shot at Hurricane Harvey before landfall.
Hey Sully!
Didn't know you were back.
I'm personally rooting for them all to remain tropical storms. The streak'll be broken sometime probably (the streak is of a hurricane in every season is going back to the onset of the First World War, after all), but hope it continues for a while longer.
Pretty incredible numbers, for August 19th....
That has a bias. Its impossible the low is around 10N
Dude you asked that like 2 hours ago. Go back to your blog, I am sure the toes are waiting!!!
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 19 AUG 2011 Time : 164500 UTC
Lat : 16:08:40 N Lon : 83:56:35 W
CI# /Pressure/ Vmax
3.0 /1000.5mb/ 45.0kt
Final T# Adj T# Raw T#
3.0 3.4 3.6
Center Temp : -24.8C Cloud Region Temp : -53.9C
Scene Type : CURVED BAND with 0.79 ARC in LT GRAY
Positioning Method : FORECAST INTERPOLATION
Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC
Tno/CI Rules : Constraint Limits : 0.7T/6hr
Weakening Flag : OFF
Rapid Dissipation Flag : OFF
C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : N/A
- Environmental MSLP : 1011
I understand all about "centers" in weak systems like this. I see a distinct rotation near 51W but no point rehashing it I suppose.
Wow
Lower in deed!
That would throw a stick in the spokes of the models.
I wish you had not shown me that.....
Not really...The convection has been on the NW side for some time now and it's confusing people in that they think the center is farther NW.
Viewing: 451 - 501
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