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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Whattta ya got there? Seeing those low level clouds?
I see lots going on in the Atlantic.
Looks like 97 may take a death ride over the island ridges to me?
ABNT20 KNHC 201157
TWOAT
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SAT AUG 20 2011
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM HARVEY...LOCATED ABOUT 35 MILES WEST-NORTHWEST OF ROATAN
HONDURAS.
A LARGE TROPICAL WAVE IS LOCATED ABOUT 400 MILES EAST OF THE LESSER
ANTILLES...MOVING WESTWARD TO WEST-NORTHWESTWARD AT ABOUT 20 MPH.
THE ASSOCIATED SHOWER ACTIVITY SHOWS SIGNS OF ORGANIZATION...AND
SURFACE OBSERVATIONS INDICATE THAT PRESSURES ARE LOW IN THE AREA.
HOWEVER...THERE IS NO EVIDENCE OF A SURFACE CIRCULATION AT THIS
TIME. SLOW DEVELOPMENT OF THIS SYSTEM IS LIKELY...AND A TROPICAL
DEPRESSION COULD FORM OVER THE NEXT COUPLE OF DAYS. THIS SYSTEM
HAS A HIGH CHANCE...80 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS. INTERESTS IN THE LESSER ANTILLES...THE
VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE PROGRESS OF
THIS DISTURBANCE. LOCALLY HEAVY RAIN AND GUSTY WINDS ARE LIKELY
OVER THE LESSER ANTILLES LATER TODAY THROUGH SUNDAY...AND OVER THE
VIRGIN ISLANDS AND PUERTO RICO BY SUNDAY NIGHT. AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE THIS
SYSTEM LATER THIS AFTERNOON...IF NECESSARY.
A LARGE AND ELONGATED AREA OF LOW PRESSURE CENTERED OVER THE CAPE
VERDE ISLANDS IS PRODUCING DISORGANIZED SHOWER AND THUNDERSTORM
ACTIVITY. THE LOW IS MOVING INTO AN AREA OF UPPER-LEVEL WINDS AND
SEA SURFACE TEMPERATURES THAT ARE LESS CONDUCIVE FOR DEVELOPMENT.
THIS SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS. LOCALLY HEAVY RAINS AND
GUSTY WINDS SHOULD CONTINUE TO AFFECT PARTS OF THE CAPE VERDE
ISLANDS THROUGH THE REST OF TODAY.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER BEVEN
And with that, I'm out to catch up on some sleep. Later all.
It looks like it's trying to get around there... saw it come together in the first couple of daylight frames... interesting to see if it holds and the convection can get around it.
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SAT AUG 20 2011
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM HARVEY...LOCATED ABOUT 35 MILES WEST-NORTHWEST OF ROATAN
HONDURAS.
A LARGE TROPICAL WAVE IS LOCATED ABOUT 400 MILES EAST OF THE LESSER
ANTILLES...MOVING WESTWARD TO WEST-NORTHWESTWARD AT ABOUT 20 MPH.
THE ASSOCIATED SHOWER ACTIVITY SHOWS SIGNS OF ORGANIZATION...AND
SURFACE OBSERVATIONS INDICATE THAT PRESSURES ARE LOW IN THE AREA.
HOWEVER...THERE IS NO EVIDENCE OF A SURFACE CIRCULATION AT THIS
TIME. SLOW DEVELOPMENT OF THIS SYSTEM IS LIKELY...AND A TROPICAL
DEPRESSION COULD FORM OVER THE NEXT COUPLE OF DAYS. THIS SYSTEM
HAS A HIGH CHANCE...80 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS. INTERESTS IN THE LESSER ANTILLES...THE
VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE PROGRESS OF
THIS DISTURBANCE. LOCALLY HEAVY RAIN AND GUSTY WINDS ARE LIKELY
OVER THE LESSER ANTILLES LATER TODAY THROUGH SUNDAY...AND OVER THE
VIRGIN ISLANDS AND PUERTO RICO BY SUNDAY NIGHT. AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE THIS
SYSTEM LATER THIS AFTERNOON...IF NECESSARY.
A LARGE AND ELONGATED AREA OF LOW PRESSURE CENTERED OVER THE CAPE
VERDE ISLANDS IS PRODUCING DISORGANIZED SHOWER AND THUNDERSTORM
ACTIVITY. THE LOW IS MOVING INTO AN AREA OF UPPER-LEVEL WINDS AND
SEA SURFACE TEMPERATURES THAT ARE LESS CONDUCIVE FOR DEVELOPMENT.
THIS SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS. LOCALLY HEAVY RAINS AND
GUSTY WINDS SHOULD CONTINUE TO AFFECT PARTS OF THE CAPE VERDE
ISLANDS THROUGH THE REST OF TODAY.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER BEVEN
Obama's June trip to Puerto Rico was the first by a sitting US President since Kennedy. That means no visits from Nixon, Ford, Reagan, Bush I, or Bush II. Perspective always helps.
97L looks very impressive this morning. I'd put the center at roughly 14.8N/54.5W. If that convection can consolidate, we should see a TD by tomorrow, if not today.
I see that ATCF has deactivated 99L (though NHC still has the floater up); can we assume that means 98L won out after all?
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SAT AUG 20 2011
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM HARVEY...LOCATED ABOUT 35 MILES WEST-NORTHWEST OF ROATAN
HONDURAS.
A LARGE TROPICAL WAVE IS LOCATED ABOUT 400 MILES EAST OF THE LESSER
ANTILLES...MOVING WESTWARD TO WEST-NORTHWESTWARD AT ABOUT 20 MPH.
THE ASSOCIATED SHOWER ACTIVITY SHOWS SIGNS OF ORGANIZATION...AND
SURFACE OBSERVATIONS INDICATE THAT PRESSURES ARE LOW IN THE AREA.
HOWEVER...THERE IS NO EVIDENCE OF A SURFACE CIRCULATION AT THIS
TIME. SLOW DEVELOPMENT OF THIS SYSTEM IS LIKELY...AND A TROPICAL
DEPRESSION COULD FORM OVER THE NEXT COUPLE OF DAYS. THIS SYSTEM
HAS A HIGH CHANCE...80 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS. INTERESTS IN THE LESSER ANTILLES...THE
VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE PROGRESS OF
THIS DISTURBANCE. LOCALLY HEAVY RAIN AND GUSTY WINDS ARE LIKELY
OVER THE LESSER ANTILLES LATER TODAY THROUGH SUNDAY...AND OVER THE
VIRGIN ISLANDS AND PUERTO RICO BY SUNDAY NIGHT. AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE THIS
SYSTEM LATER THIS AFTERNOON...IF NECESSARY.
A LARGE AND ELONGATED AREA OF LOW PRESSURE CENTERED OVER THE CAPE
VERDE ISLANDS IS PRODUCING DISORGANIZED SHOWER AND THUNDERSTORM
ACTIVITY. THE LOW IS MOVING INTO AN AREA OF UPPER-LEVEL WINDS AND
SEA SURFACE TEMPERATURES THAT ARE LESS CONDUCIVE FOR DEVELOPMENT.
THIS SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS. LOCALLY HEAVY RAINS AND
GUSTY WINDS SHOULD CONTINUE TO AFFECT PARTS OF THE CAPE VERDE
ISLANDS THROUGH THE REST OF TODAY.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER BEVEN
7:00 AM CDT Sat Aug 20
Location: 16.6°N 87.0°W
Max sustained: 60 mph
Moving: W at 12 mph
Min pressure: 994 mb
Looks like 97L still has three options - under, over, or through - though the under has been under emphasised in the last couple of model runs.... I'm looking to see exactly where they call it, because that'll make a big difference in how much interation with land it has...
TIME
Morning Nea..
Well said... on all fronts.
We've been looking at the possibility of some low level clouds trying to get around roughly where you have a center in the last couple of 97L visual frames.
Your thoughts?
Johnson. Carter.
How did you get to that conclusion? Lol.
That over or under would have to be 30-50 miles of PR, DR, & Cuba...Which is certainly possible. Just can't help but think about what we've seen those mountain ranges do to so many storms. ie...Ernesto,
...and Clinton, yes. And I see you missed the point of my response. ;-)
Anyone see that three people were killed in flash flooding in Pittsburgh last evening? Apparently a pair of storms dumped several inches in some areas. Sad...
There was a landfalling TS, it was called Don and TX eat it up upon arrival.
INV/XX/97L
MARK
14.71N/55.15W
08L/TS/H/CX
APPROACHING LANDFALL
TV mets, models, experts on the blog seem to want to ignore it this time. With Harvey all the talk was - will it survive Haiti. I'm not hearing it with 97L.
.BUT QUICKLY
BECOME LARGE SURROUNDING THE STRONG AND COMPLEX UPPER TROUGH OVER
THE GULF OF ALASKA...AND ALSO IN THE CARIBBEAN SEA/GULF OF MEXICO
DUE TO INCREASINGLY DIFFERENT TRACK FORECAST FOR THE TROPICAL WAVE
CURRENTLY ENTERING NEARING THE LEEWARD ISLANDS. TO ADDRESS THESE
INCREASINGLY LARGE DIFFERENCES...WILL LIKELY TRANSITION QUICKLY TO
EITHER THE 00Z GEFS MEAN AND/OR ECMWF ENSEMBLE MEAN FOR THE
PRELIMINARY PRESSURES/FRONTS FOR DAYS 3-7. MODELS HAVE TRENDED
SLIGHTLY TO THE RIGHT OF PRIOR FORECASTS WITH THE TROPICAL WAVE
NEARING THE LEEWARD ISLANDS WITH THE 00Z OPERATIONAL ECMWF CLOSEST
TO THE DETERMINISTIC CONSENSUS AND GLOBAL ENSEMBLE MEANS.
MEANWHILE..THE 00Z GFS IS SLIGHTLY TO THE RIGHT AND FASTER WITH
THE UKMET/CANADIAN TO THE LEFT BRINGING THE WAVE INTO THE CENTRAL
GULF OF MEXICO BY NEXT FRIDAY. FOR NOW...WILL USE THE LATEST
COORDINATION POINTS AGREED UPON FROM THE NHC AND EXTRAPOLATE ONE
DAY FORWARD FOR THE NEW DAY 7 POINT...WHICH WILL PLACE IT IN THE
EASTERN GULF ON SATURDAY WHICH IS JUST LEFT OF THE 00Z ECMWF
POSITION.
JAMES
A week eye appears tobe forming in the last few frames
I live in the Tampa area and to be honest, I'm not worried. Look at historicals - Storms coming from this direction never make a direct hit. The closest we might come to impact is a storm crossing the state.
If you look at just the last four frames of the RGB loop (where the sun is shining upon it), it does appear that low-level clouds are trying to make their way towards the primary blob. It'll be interesting to see watch 97L today; my favorite part of following TCs is this, the gestational stage. You know, the whole "will he, or won't he?" thing. It's fascinating to me--and I'm obviously not alone in that.
You must be the only one who got your point.
And two were children. They're saying a fourth missing person is being presumed dead now. Very sad. They were unable to get to the vehicle in time.
Viewing: 3801 - 3851
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