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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NOUS42 KNHC 201500
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1100 AM EDT SAT 20 AUGUST 2011
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 21/1100Z TO 22/1100Z AUGUST 2011
TCPOD NUMBER.....11-081
I. ATLANTIC REQUIREMENTS
1. SUSPECT AREA (NEAR LESSER ANTILLES)
FLIGHT ONE -- TEAL 72
A. 21/1200Z,1800Z
B. AFXXX 0209A CYCLONE
C. 21/1100Z
D. 15.8N 61.8W
E. 21/1130Z TO 21/1800Z
F. SFC TO 10,000 FT
FLIGHT TWO -- TEAL 73
A. 22/0000Z,0600Z
B. AFXXX 0309A CYCLONE
C. 21/2300Z
D. 16.5N 65.00W
E. 21/2330Z TO 21/0600Z
F. SFC TO 10,000 FT
2. OUTLOOK FOR SUCCEEDING DAY:
A. CONTINUE 6-HRLY FIXES ON SYSTEM IF STILL A THREAT.
B. POSSIBLE G-IV SURVEILANCE MISSION FOR 23/0000Z.
3. REMARK: IF A CLOSED CIRCULATION IS NOT FOUND ON TODAY'S
MISSION NEAR THE ANTILLES, THE 21/1200Z MISSION WILL
SLIP TO A 21/1800Z INVESTIGATIVE MISSION
Good Morning Levi!
Looking forward to your input.
:)
despite all of this consistency from the models the last few days, all it will take is one run of one model to either kill the system off or bring it into Florida as a weak system; then some will come in here and question the models and say this storm is being hyped lol
you know its coming, just preparing all of you for the inevitable
99 hours out system heading north towards the bahamas...
The boundaries of higher rainfall is simply where the data cannot be trusted and, sometimes, wild fluctuations can happen.
(Not to mention the notion of measuring winds of an outflow boundary near intense convection, not representative of sustained winds in a TC).
Hi Levi.
low shear across the basin
Hmm...interesting stuff.
108 hours system moves wnw along north cuba coast
LOL - that is hilarious
Yeah and it looks like the anti-cyclone that was displaced to the southeast of 97L yesterday has caught up to it as well. That should help it throw off the dry air and any heavier shear areas it may encounter as long as they move in tandem.
Does non-insignificantly mean significantly? ;)
I have no idea where you came uo with this. The 850mb vortex runn shows the circulation actually rather north in the islands coming in and barely missing puerto rico. Going thru the islands and exiting, hitting S. Florida. Just observing the model...run which is actually slightly north and east of the last run.
If that's what he meant, My Bad
Im sure some will recall after Katrina crossed floridaand was a TS, How long did it take her to get really ramped up again? Of course crossing Florida is not the same as crossing Cuba,depending on speed and pool of hot water north of cuba????????????
Heavy storms in the strongest part, but we need to get a mid level circ to the surface
Because, GFS has it come up the middle of the state, and even jogs over to catch far eastern pan handler's. A little something for everyone from the Islands to NYC and beyond. Wow!
Let's hope it does not pan out or hold it's intensity. Is that even possible?
But with this stated, it has to end up somewhere, and no one seems to be thinking an eleventh hour swing out to sea. Right?
Katrina was actually intensifying as it crossed Miami-Dade county...I don't know if it ever lost strength while crossing Florida.
Viewing: 4551 - 4592
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