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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dont get mad at me! get mad at the satelite pics
What are you trying to say? Just say "I don't know where it's going...
LOL. Either one is going to knock over a few things heading for the door.
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 20 AUG 2011 Time : 124500 UTC
Lat : 16:27:36 N Lon : 87:07:08 W
CI# /Pressure/ Vmax
4.2 / 985.1mb/ 69.8kt
Final T# Adj T# Raw T#
4.2 4.2 4.4
Center Temp : -74.9C Cloud Region Temp : -73.7C
Scene Type : UNIFORM CDO CLOUD REGION
Positioning Method : FORECAST INTERPOLATION
Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC
Tno/CI Rules : Constraint Limits : 1.2T/12hr
Weakening Flag : OFF
Rapid Dissipation Flag : OFF
C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : 33km
- Environmental MSLP : 1012mb
Satellite Viewing Angle : 23.8 degrees
Geez, notice the use of the word "starting". You mad?
true that.
always expect the unexpected
Morning kman, Aussie, & GR
That is what I am thinking, but the track of 97L will be the tale of the tape. It is also chugging along right now at about 20 mph. Should it slow down as it seeks the weakness in the ridge and bump over 50-100 miles further west after encountering Cuba, then it is is some very hot water and RI might happen.
It is safe to downcast it, putting the FLAG on both the weakening and rapid dissipation flag because it may interact with the Yucatan.
No closed low there but the swath was taken almost 3 hours ago. 97L certainly looks to be capable of closing off a low before 63W which is about 500 miles farther West from the present position.
Wanna come spend next weekend at the beach with me?
I know it is not going to Texas or Louisiana.
In S. Fl they are all saying it has to be watched closely but they haven't raised the doom gong yet...just showing the models and telling us we will know more in the next couple of days
Just some cyclonic curvature on the north side, however lots of contaminated barbs. ASCAT made a pass ~9AM EDT so that should show up in an hour or so, if it even caught the storm which ASCAT seems to mostly miss storm centers.
What the....?!
We all will know more in a few days. BTW is this normal TV or cable TV?
144 hours
168 hours
Hopefully we get a definitive answer from the hurricane hunters this afternoon, if NHC does not cancel the mission. The 8AM EDT TWO had the ole... investigate if necessary. Organization looks good enough to me to send the plane.
97L developes sooner than expected? It's come all the way from Africa, is almost at the Antilles, and it's still nothing more than a fuzzy blob, with very little evidence of banding or rotation. Don't Cape Verde storms usually look like tropical storms by this time?
So far, it's doing the same as the rest of this year's systems. Looks like there's something out there hindering development that we're in the dark about. Dr Masters mentions low vertical instability in his blog.
The regular channels. Just watched channel 10 but also saw channel 4 a little while ago.
looks to me (imo) like its going to enter the carib at 15.5 to 16.0N or so. Sat seems to indicate that its near 14.9 / 55.2 now May already be moving north of west or wnw. Do you think thats a low entry point. Thats near the northern leeward islands
Good to hear you're OK.
Correct me if I'm wrong but are we not just starting to ramp up the CV season? Also, historically we are still about 3 wks away from the peak of hurricane season...
Considering they sent a plane into 93L/pre Harvey when clearly there was no surface low they should send one to 97L. In fact when the plane first went into 93L it was sitting right on top of a buoy with high and rising surface pressure. They didn't stay long though LOL
When Cantore hits the Beach...
Then at 20th day of the month at 13:27Z, Minimum Sea Level Pressure: 1004mb (29.65 inHg).
Harvey went up 5mb in 1hr? Anyone else think this is a bit strange when Harvey looks like he's intensifying?
Viewing: 4051 - 4101
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