Danny weakens further; 94L worth watching
Tropical Storm Danny continues to weaken, and may merely be a tropical depression. Data from the Hurricane Hunters early this morning showed top winds of just 40 mph at the surface, and satellite intensity estimates of Danny's strength are now rating the storm a tropical depression. Danny looks very disorganized on satellite imagery (Figure 1), with the low-level circulation center exposed to view. There is no heavy thunderstorm activity near Danny's center, and only a small area of heavy thunderstorms lying several hundred miles east of the center.
Figure 1. Morning satellite image of Danny, showing the exposed swirl of clouds where Danny's center is, well displaced from the heaviest thunderstorm activity to the east.
The forecast for Danny
With wind shear at 15 knots this morning, and forecast to increase to 20 knots tonight and 30 knots Saturday morning, is is unlikely Danny will be able to strengthen to more than a 50 mph tropical storm. Dry air from the upper-level low that has been keeping Danny disorganized continues to be a problem for the storm, as well. The GFDL and HWRF models continue to insist Danny will strengthen to a strong tropical storm or weak Category 1 hurricane, but this seems very unrealistic given Danny's current struggles. With Danny's heavy thunderstorms all on the east side of the storm, it is unlikely that New England will feel tropical storm force winds from Danny when it scoots past on Saturday. Large swells from Danny creating high surf along the beaches of New England will be the primary hazard from the storm.
Massachusetts hurricane history
Two tropical storms have affected Massachusetts in the past decade, though neither of these storms brought sustained winds of tropical storm force (39 mph) to the state. Tropical Storm Beryl of 2006 just missed Cape Cod as a weak tropical storm with 45 mph winds. Beryl brought wind gusts to tropical storm force to Nantucket Island, and a 1 foot storm surge. Tropical Storm Hermine hit southeast Massachusetts on August 31, 2004, as a minimum-strength tropical storm with 40 mph winds. No land stations in Massachusetts reported tropical storm force winds during Beryl. The last time Massachusetts measured tropical storm force winds was in 1991 during Hurricane Bob, which hit Rhode Island as a Category 2 hurricane. Provincetown, Massachusetts measured sustained winds of 98 mph, gusting to 115 mph, and Buzzard's Bay received a 15 foot storm surge.
Figure 2. Tropical wave 94L, a few hundred miles west of the Cape Verdes Islands.
Invest 94L
A well-organized tropical wave (94L) lies a few hundred miles west-southwest of the Cape Verdes Islands. This disturbance has shown little change this morning. This morning's QuikSCAT pass shows a complete circulation, elongated in the east-west direction, with top winds of 30 mph. Satellite imagery shows only a small amount of heavy thunderstorm activity near the circulation center, but considerable thunderstorm activity south of the center. Shear is low, about 10 knots, and is expected to remain low to moderate, 5 - 15 knots, over the next five days. The waters are warm enough to support development, 28°C, and are expected to remain in the 27 - 28°C range over the next five days. The dry Saharan Air Layer (SAL) lies about 200 miles to the north and west of 94L, and it appears from water vapor satellite imagery that a modest amount of dry air from the SAL is now being ingested into the storm, slowing development. Dry air will continue to slow development until 94L's heavy thunderstorm activity can moisten the atmosphere enough to shield the storm from the Saharan Air Layer. NHC is giving 94L a medium (30 - 50% chance) of developing into a tropical depression by Sunday. The GFDL and SHIPS models both predict 94L will be a Category 1 hurricane five days from now. However, the HWRF model does not develop 94L. Most of the models predict 94L will take a significant northward jog 3 - 5 days from now, in response to a strong trough of low pressure passing to the north (this is the same trough of low pressure that will be recurving Danny out to sea). It is then probable that 94L will be forced to the west again as the high pressure ridge steering the storm builds back in, and 94L will likely be a few hundred miles northeast of the Northern Lesser Antilles Islands seven days from now.
I'll have an update this afternoon.
Jeff Masters
Reader Comments
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Looks like a very wet weekend for some on the East Coast
Watch this loop with radar on. One layer of clouds goes one way, one goes another, and I think the rain is coming from both. Strangest stuff I've seen.
(longer Pink-looking one is XTRP)
I have not been on much lately but have started to pay close attention to 94L.
There are several important factors at work in respect of this feature but they are not all conducive to rapid development. On the plus side you have warm water, an anticyclone overhead and little in the way of shear ahead. On the negative side you have the fast forward speed of 23 mph, dry air close by and the inhibition caused by being tied into the ITCZ.
The net effect of all this IMO is that 94L will not likely become a TD before reacing 50W assuming it does develop. If that happens, the trough that is supposed to lift it out will probably pass it by.
There is, IMO , a greater than 50% chance of 94L entering the Caribbean, probably around 16 or 17N depending on when it develops as a cyclone and how quickly the intensity ramps up. The low center is already closing in on 40W very quickly and the models have already abandoned the abrupt right turn to the N.
I am expecting each successive model run to trend further and further W over the next 24 hours so we will see how all of this plays out.
I sooooo hope you are right!
I expect only slow development - possibly a storm by Sunday or Monday.
Reasons for slow development:
1. Still in the ITCZ - most of the convergence is associated with this and is linear
Surface Convergence
2. Vorticity also linear - rotation not around a singular point but more along a line with strong southerlies south of the ITCZ and strong easterlies to the north of the ITCZ.
850 Vorticity
3. Super strong 700/850 easterly flow will make it tough for a circulation to wrap up. The GFS show only slow westward progression with its low. The discrepancy in how fast the flow is and expected motion of the low is weird. This would either suggest the area will be sheared heavily in the low to mid-levels or it will race west and the models are way wrong.
Hey Drak!What are your thoughts on the track for this one?
It means Dr. Masters has a new blog.
very stormy here in wilmington..would this be because of the ull or Danny outerbands?
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