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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Well I mean that set up has to change eventually (I mean theoretically it does) Maybe the models are hinting at that in the longer range.
Nightly channel is now 9.0a1 2011-08-19
Any thoughts on Harvey, Taz?
Couldn't have said that any better. Emily most likely helped move, at least some, of the drier air out of the way for the train we are seeing and will continue to see for the next few weeks
Absolutely...very small but vigorous central core developing quickly, usually a warning sign of rapid intensification. The environment is very conducive for it and it is well organized all the way down to the lower levels.
Vertical Shear is favorable across the entire Atlantic basin.
Because the ensembles don't show the Texas ridge coming back directly over the state or near as strong as it has been during the next two weeks, and similar historical patterns to 2011, something I have spoken about often this season, foretell the Texas ridge weakening and moving out of the way a little bit more during the peak months of the season. In my opinion Texas may still be the hardest gulf state to hit this entire season, but they could still get a storm before it's over.
97L track seems to match what I remember of 93L (now Harvey) and Emily tracks. I still think 97L will enter the Caribbean at around 14N between St. Lucia and Martinique.
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/ carib/gfs/18/model_s.shtml
Levi, what is your opinion about Harvey? If it isn't undergoing rapid intensification, I believe it should soon.
NATIONAL WEATHER SERVICE FORT WORTH TX
245 PM CDT FRI AUG 19 2011
.DISCUSSION...
...VERY HOT WEATHER WILL CONTINUE THROUGH THE WEEKEND...
AFTER RUNNING THE NEW DATA...WE HAVE EXTENDED AND SLIGHTLY
EXPANDED THE CURRENT HEAT ADVISORY ACCORDING TO EXPECTED HOT
TEMPERATURES AND WHERE HUMIDITY STAYS UP HIGH ENOUGH TO PUSH HEAT
INDICES AT/ABOVE 105 DEGREES F. UPPER HIGH TO REMAIN DOMINANT
ACROSS NORTH TEXAS THROUGH THE WEEKEND AND THOUGH SOME RICHER
MOISTURE IS TRAPPED ACROSS EAST TX...IT APPEARS THE STRONG
SUBSIDENCE WILL INHIBIT ANY ISOLATED DEVELOPMENT ACROSS OUR FAR
EASTERN COUNTIES THROUGH SUNDAY.
A WEAK FRONT WILL EASE SOUTH INTO CENTRAL/SOUTHERN OKLAHOMA BY
SUNDAY NIGHT INTO EARLY MONDAY MORNING WITH HELP FROM ANY OUTFLOW
FROM NOCTURNAL THUNDERSTORMS ACROSS KANSAS AND NORTHERN OKLAHOMA.
THIS WEAK CONVERGENCE AREA MAY INDUCE SOME ISOLATED SHOWERS AND
THUNDERSTORMS JUST NORTH OF THE RED RIVER...BUT DO NOT HAVE ANY
CONFIDENCE AT THIS TIME THAT ANY ACTIVITY WILL MAKE IT SOUTH OF THE
RIVER INTO TEXAS WITH BEST FORCING ALOFT BEING CONFINED TO THE
OKLAHOMA/KANSAS BORDER AND POINTS NORTH.
FOR NEXT WEEK...MODELS ALL CONTINUE THE TREND OF A DEEPENING UPPER
TROUGH OVER THE EASTERN CONUS...WITH OUR CURRENT UPPER HIGH SHIFTING
BACK WEST ACROSS WEST TEXAS INTO THE DESERT SOUTHWEST. WE SHOULD
CONTINUE OUR TREND OF DAYS OVER THE CENTURY MARK...AS WE SLOWLY INCH
CLOSER TO THE NUMBER OF 100-DEGREE DAYS SET IN 1980. LATEST 12Z RUNS
OF THE GFS AND ECMWF MODELS INDICATE WEAK NORTHWEST FLOW ALOFT COULD
GRAZE EASTERN SECTIONS OF NORTH TEXAS BY THE LATTER HALF OF THE WEEK
AND POSSIBLY BRING IN A FEW...WEAK BACKDOOR FRONTS INTO THE ARKLATEX
REGION. AT THIS TIME...THERE REMAINS TOO MANY UNCERTAINTIES
REGARDING FORCING AND MOISTURE TO INTRODUCE ANY LOW RAIN CHANCES AND
WILL CONTINUE A DRY/HOT FORECAST WITH HIGHS BETWEEN 100-105 DEGREES.
AS FOR ANY RELIEF REGARDING THE TROPICS...THE NEXT WEEK DOES NOT
LOOK OVERLY PROMISING. NEWLY NAMED TROPICAL STORM HARVEY WILL MOVE
DUE WEST INTO CENTRAL AMERICA THE NEXT 24-48 HOURS. AN EASTERLY
WAVE FORECASTED BY MODELS TO STRENGTHEN INTO POSSIBLY IRENE LATER
THIS WEEK INTO NEXT WEEKEND IS BEING SHOWN TO BE PICKED UP BY THE
EASTERN CONUS UPPER TROUGH AND LIFTED NORTH EITHER ALONG THE WESTERN
FLORIDA GULF COAST...OR INTO THE FLORIDA PANHANDLE DEPENDING ON
WHICH MODEL YOU BELIEVE. THOUGH THIS WON`T BRING RAIN INTO NORTH
TX...IT COULD BRING SOME RELATIVELY DRIER AND SLIGHTLY COOLER AIR
INTO THE AREA BY NEXT WEEKEND.
Upper air environment will be better the further S it tracks in the Caribbean. But even a more N-erly track will only encounter shear of 10-15 kts at best.
maybe so, seems it would have to let up sometime. We shall see...
Thats why I posted the loop link earlier and said play it in reverse.
The expansion was very evident that way.
Lol or even worse, pulls a Don on us!
ok, I see. Thanks Levi
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 19 AUG 2011 Time : 204500 UTC
Lat : 16:29:34 N Lon : 84:39:51 W
CI# /Pressure/ Vmax
3.5 / 994.1mb/ 55.0kt
Final T# Adj T# Raw T#
3.5 3.5 3.8
pressure fall wind rise...
97L looking decent at the moment but a lot of dry air between it and the Antilles at the moment so I am not sure that NHC is going to up the percentages substantially between now and Sunday unless the moisture field significantly expands before then to help fight off intrusion IMHO....
that also indicates that winds are 63 MPH...
lol, what do you think it has been doing since it left Africa? It has had A LOT of dry air to deal with, and now it is beginning to lessen on the system, which is why the system has increased in organization over the past few hours.
Dmin should be occurring right now (or has already passed) as the airmass over water is the most stable due to temperature differentials between the water and atmosphere is the least. The Dmax, which will occur in the pre-dawn hours when there is more instability in the atmosphere between water and airmass above the water is greatest. Therefore, we should begin to see a steady increase in convection as the evening and overnight wears on.
Obvsiously, the NHC doesn't! 97L should cross the islands further north and impact PR according to their surface forecast. Look :
then :
ONCE AGAIN, GFS IS TOO MUCH SOUTH!
Proves the watched pot never boils.
No, the NHC is too far north.
Land interaction is going to be the wild card with 97. Of course the strength of the late weak trough is also going to become a player to see how much of a weakness it creates. These two features will be the main drivers for where the system ultimately ends up.
.EXTENDED FORECAST...
FOR THE MIDDLE TO END OF NEXT WEEK...THE FORECAST WILL DEPEND ON
THE STRONG TROPICAL WAVE ABOUT 800 MILE EAST OF THE LESSER
ANTILLES. AT THIS TIME...THE NATIONAL HURRICANE CENTER IS
FORECASTING THE TROPICAL WAVE TO MOVE TO THE WEST TO NORTHWEST
TOWARDS THE REGION. HOWEVER...THERE IS CONSIDERABLE UNCERTAINLY
OF THE DEVELOPMENT AND POSITION OF THE TROPICAL WAVE DURING THIS
TIME...THE FORECAST WILL REMAIN UNCHANGED WITH THE TYPICAL SUMMER
TIME WEATHER PATTERN. PEOPLE OF SOUTH FLORIDA NEED TO CONTINUE TO
MONITOR THE LATEST TROPICAL WEATHER OUTLOOKS FROM THE NATIONAL
HURRICANE CENTER ON THIS TROPICAL WAVE.
They are experts ;-)
August is living up to its reputation as the beginning of the busiest part of hurricane season. Tropical Storm Harvey is threatening Honduras and Nicaragua, while Invests 98 and 99 are swirling off the African Coast, Tampa Bay residents need to focus for the moment on the Invest 97 which is about halfway between the Cape Verde Islands and the Lesser Antilles. According to Weather Underground founder and hurricane expert Dr. Jeff Masters "Computer models have shown an unusual amount of agreement in developing 97L over the past few days."
The spaghetti chart of computer model course projections show a definite long term trend toward courses that could threaten Florida late next week, but Masters notes that the course projections are combined with some favorable conditions for development. "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." On the other hand there is a lot of dry air in the region and there are any number of land masses that could weaken or destroy the storm.
Despite a healthy number of tropical cyclones and areas of interest for forecasters to watch, we still have not had a storm make it to hurricane strength so far this year. A fact that Masters chalks up to an unusually large amount of stable air that inhibits the ability of thunderstorms to grow vertically. You can see Masters' technical analysis and complete blog entry by clicking here.
According to Masters the real key to figuring out where Invest 97 goes is a low pressure trough that's expected to creep into the eastern U.S. How strong that trough is and how fast it moves will determine when 97 starts to turn north. An early turn could take up the east coast of Florida, a later turn could take it over the Florida peninsula or into the Gulf of Mexico. In any case we'll echo Dr. Masters' advice: now would be a good time make sure you are prepared.
Just my take.
The NAO is still only weakly positive (0.99543E-01). Not too often to you get the chance to track a storm purely based on the strength of the B/A high. This is going to be one of those cases in my opinion and the NAO explicitly deals with it's strength and that of the Icelandic low . This is deep layer steering meaning that the high will guide it to the point of weakness unobstructed. I am assuming this on the fact that 97L will reach as high as the models portray. An undeveloped weak storm would obviously be subject to the status quo trade winds and move further westward. Personally, I will start to lean further westward if we see the NAO go more positive the next few days, if not, my thoughts are from west FL coast eastward.
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