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
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Evening guys?
No, the TX ridge will be too strong for 97L to keep going west.
likely not west of NOLA
Nice thunderstorms over Central Africa. About to emerge off the coast in a few days.
Yeh - that it's not going to make it all the way over to Texas.
24 hour gym :)
Transmitted: 20th day of the month at 01:56Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 308)
Storm Number & Year: 08L in 2011
Storm Name: Harvey (flight in the North Atlantic basin)
Mission Number: 4
Observation Number: 15
A. Time of Center Fix: 20th day of the month at 1:37:50Z
B. Center Fix Coordinates: 16°09'N 84°59'W (16.15N 84.9833W) (View map)
B. Center Fix Location: 232 miles (373 km) to the ESE (114°) from Belize City, Belize.
C. Minimum Height at Standard Level: 3,077m (10,095ft) at 700mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 39kts (~ 44.9mph)
E. Location of the Estimated Maximum Surface Wind: 24 nautical miles (28 statute miles) to the W (264°) of center fix
F. Maximum Flight Level Wind Inbound: From 13° at 31kts (From the NNE at ~ 35.7mph)
G. Location of Maximum Flight Level Wind Inbound: 31 nautical miles (36 statute miles) to the W (266°) of center fix
H. Minimum Sea Level Pressure: 997mb (29.44 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 7°C (45°F) at a pressure alt. of 3,064m (10,052ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 14°C (57°F) at a pressure alt. of 3,056m (10,026ft)
K. Dewpoint Temp & Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 700mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile
Remarks Section - Remarks That Were Decoded...
Maximum Wind Outbound: 53kts (~ 61.0mph) in the northeast quadrant at 1:39:00Z
Maximum Flight Level Wind: 53kts (~ 61.0mph) in the northeast quadrant at 1:39:00Z
Remarks Section - Additional Remarks...
GOOD SPIRAL BAND NEARLY PINPOINTED FL CNTR
MAX SFC WIND OUTBOUND 46 KTS, NE QUAD, 01:39:30Z
FQT LTG IN CONVECTION NEAR FL CNTR
Really? Here in VA? Thanks. LOL we don't need it in terms of rainfall, we're just fine.
pretty sure that is the very powerful wave Levi eluded to the other day
Still, gym? 10PM?
It is also important to note that the global models to not show significant deepening of the system until 72 hours from now. That is a long time, and it is perfectly reasonable given the broadness of the wave we are dealing with right now. Development should not be expected to follow an accelerated schedule at this time.
BE WORRIED!?!?!
It is looking VERY good on satellite. It really impresses me.
Link
I mentioned it first!
lol.
That's actually smart. Go when there isn't a lot of people.
the models do pick up on a system comin from africa in a few days
Must be one heck of a commitment.
the actual center of 99L is actually quite a bit northeast of that convection. In fact, it looks like 98L is beginning to merge with 99L.
Saying that though, once 98L and 99L merge, this could begin to become a tropical cyclone.
East Africa Satellite
I mentioned it last week.
Thanks Levi, Just got in and your informative post is good news...
...After me :P
Levi takes 3rd place in this one:
1.) Me
2.) Grothar
3.) Levi32
I live in Bucharest, Hungary....what are the chances 97L affects me?
Due to the fact that high pressure should be centered somewhere near the rockies, it will be hard to get the high to move far enough westward to make landfall SW La/Texas. If the Gulf Coast needs to worry about this, which they do, Mississippi and points west for a landfall point seem more likely.
Yes, they do. Looks like a few may be lining up.
It's ok. I don't care that much about watching waves out in central Africa when we have problems closer to home.
nop
notice this system didnt move up form 40 mph to 45 mph until 4 days after it formed hopefully 97l dosent do this
LOL. Link
My friend that is yesterday's 18Z i believe i just checked today's 18z which targets the NE Gulf Coast near Florida!!!Link
Incorrect. The current GFS 18z run has it making an approach to FL Panhandle .
Yeah, that's a good point.
lol.
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