Tropical Storm Chris; August hurricane outlook, part II

By: Dr. Jeff Masters , 11:37 AM GMT on August 01, 2006

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It's August in the tropics, the first of the peak months of hurricane season. Befitting the arrival of August comes the arrival of Tropical Storm Chris, which formed this morning just east of the Leeward Islands. The formation of Chris came in defiance of significant adversity--wind shear was 20-25 knots last night when the storm formed into a tropical depression, and is still a rather hefty 15-20 knots. Considerable dry air lies to Chris' north, and strong upper-level winds from the north are acting to push this dry air into Chris' core, keeping the storm from intensifying much. Radar out of Martinique shows a decent band of thunderstorm to the storm's southeast and east, but no thunderstorm activity on the northwest side where shear and dry air are impacting the storm. We don't have a recent QuikSCAT pass to gauge the winds, but two passes by a satellite equipped with a microwave sensor came up with an estimate of 40 mph surface winds. The Hurricane Hunters are scheduled to visit at 2pm EDT this afternoon, so we'll know more then.

This shear and dry air will continue to affect Chris over the next two days. The shear is forecast to gradually weaken, which may allow some slow intensification. Chris must tightrope walk a very narrow path between two upper-level cold lows in order to strengthen significantly. One of these cold lows is just north of the Bahamas, and the other is northeast of Chris. These lows are forecast to move slowly west-northwest in tandem with Chris, and if Chris can stay exactly between them, low enough wind shear exists to potentially allow some strengthening. Any deviation from this scenario will put Chris under hostile wind shear, which will act to limit intensification or even dissipate the storm.

Last night's computer model runs did not start out with a very good initial picture of the current strength of Chris, and dissipated the storm within 72 hours. We need to wait until the next set of model runs based on this morning's 8am EDT (12Z) data are available before taking much stock in both the track and intensity forecasts of the models. The NOAA jet is scheduled to fly the storm tonight, so the best model data for Chris will be available Wednesday morning.

Chris will bring heavy rains and high winds to the Leeward Islands today, primarily to those islands lying to the south of the storm's center, where dry and and wind shear are less of a problem. Puerto Rico should get a good soaking on Wednesday, and after that, the prognosis is very uncertain. Chris could become a hurricane late in the week, but I put the chances of this at 10%. Dissipation is a more likely scenario, since there is so much wind shear around. The most likely scenario of all is that Chris will remain a tropical storm over the next five days.

August hurricane outlook
As we've seen repeatedly, sea surface temperatures are important for hurricane formation and intensification, but nothing happens unless the wind shear is low. When we look at wind shear, the standard measure is the wind at the upper atmosphere (200 mb, usually around 40,000 feet in altitude) minus the wind just above the surface (850 mb, or about 5,000 feet altitude). This difference in wind speed is plotted in Figure 1 for July 2006. The key feature to look at is the anomalies in the bottom portion of the plot. The entire tropical Atlantic was under higher than normal wind shear during July, with wind shear up to 6-8 meters per second over the Caribbean (12-16 knots). The only region that experienced below normal wind shear was off the coast of North Carolina. Not coincidentally, this is where July's only named storm formed (Beryl).


Figure 1. Observed wind shear for July 2006. The top portion shows the difference in wind between 200 mb and 850 mb pressure levels, and the bottom image shows the departure from normal.Image credit: NOAA's Climate Prediction Center.

What, then can we expect for wind shear in August? The long range shear forecast from NOAA (Figure 2) shows near normal wind shear over the Atlantic for the remainder of hurricane season. The latest 2-week outlook from the GFS model agrees, calling for near normal wind shear during the first half of August. Since wind shear is expected to be near normal, and SSTs should be near normal, we should expect a near normal level of hurricane activity for August. "Normal" should be placed in context with the above-normal level of hurricane activity we've been seeing since 1995. In the ten years since 1995, not including the El Nino year of 1997, the Atlantic has averaged 4.4 named storms, 2 hurricanes, and one intense hurricane in August. My prediction for August follows a similar line: 4-5 named storms, two hurricanes, and one intense hurricane. All this assumes that El Nino doesn't rear its head; the recent warming of ocean waters in the Equatorial Pacific along the coast of South America could be the prelude to an El Nino event. These events create atmospheric circulation patterns that greatly increase the wind shear over the Atlantic, significantly cutting down on hurricane activity. However, the El Nino forecast models are predicting a continuation of the current neutral El Nino condition through August and September, and it is uncommon to have an El Nino event begin at this time of year. I doubt El Nino will be a factor in this year's hurricane season.


Figure 2. Forecast wind shear July August through October 2006. Image credit: NOAA's Climate Prediction Center.

What will be the steering pattern for August?
For much of June and July, the jet stream made a dip over the eastern U.S., creating a persistent trough of low pressure. In concert with the jet stream, the Bermuda High has stayed further east than it did in 2005. The resulting steering pattern has been taking tropical waves through the Bahamas, then north along the East Coast and out to sea. Tropical Storm Beryl took this path as well. The long range forecast from NOAA's Climate Prediction Center calls for not as strong a trough of low pressure for the remainder of hurricane season. Instead, we should expect a near normal steering pattern, with all regions of the Atlantic under their usual risk of hurricane strikes. However, the latest 2-week GFS model forecast is calling for a continuation of the June and July steering pattern, but with a somewhat weaker trough over the Eastern U.S. Thus, I am forecasting that the entire East Coast of the U.S. will have a higher than average risk of hurricane strikes in August, and the Gulf Coast will have a lower than average risk. The highest risk area of the East Coast will probably be North Carolina and South Carolina. As far as the actual percentage risks, I'll leave that up to Dr. Bill Gray's forecast team at Colorado State, who will be putting out their updated Atlantic hurricane season forecast on Thursday, August 3.

Jeff Masters

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1251. crazydave52
2:24 AM GMT on August 02, 2006
Thanks Weather 456:

It is a hurricane in 24 hrs. !
1250. crazydave52
2:16 AM GMT on August 02, 2006
Whats the last steering on this thing ?
1249. crazydave52
2:15 AM GMT on August 02, 2006
Boynton get your clipboard and "Sunday's best ready ! You've got work !
1248. kylejourdan2006
12:00 AM GMT on August 02, 2006
WHERE IS EVERYBODY?!
Member Since: July 18, 2006 Posts: 32 Comments: 1521
1247. kylejourdan2006
11:55 PM GMT on August 01, 2006
Winds have been upgraded to 60 MPH - so I'm giving Chris a 45% chance of becoming a hurricane in the next 6-12 hours. At the 10:30 PM, I believe that the winds will be 60-70 MPH.
Member Since: July 18, 2006 Posts: 32 Comments: 1521
1245. BoyntonBeach
9:22 PM GMT on August 01, 2006
Weather456

Chris is knocking on your door my friend, keep us up to date on how you are faring..
Member Since: July 5, 2006 Posts: 0 Comments: 1
1244. disasterworker
8:53 PM GMT on August 01, 2006
not adjuster, new employee of (now don't get all excited) FEMA. At first deployment in PA now. Watching to see if i can go home a while or to FL, not passing GO or collecting $200.
1243. KEEPEROFTHEGATE (Mod)
8:52 PM GMT on August 01, 2006
DATA SUGGESTS WINDS ARE APPROACHING 100 KMH/60 MPH CANE STATUS POSSIBLE BY 8 PM EST TRACK WILL REMAIN EXTREME NORTH LEEWARDS WESTWARDS ALONG OR JUST OFFSHORE OF P.RICO EXPECT CAT 1 STATUS TILL EXIT FROM LEEWARDS THEN CAT 2 POSS.CAT 3 FROM P.RICO ONWARD TO CAT ISLAND SHEAR IS FAILING TO AFFECT THIS STORM HURRICANE WATCH SHOULD BE ISSUED FOR P. RICO HURRICANE WARNING FOR NORTHERN LEEWARDS.THIS IS GOING TO BE A COMPACT STORM WITH A VERY SMALL EYE WHICH ARE INDICATIONS OF A VERY POWERFUL STORM YET TO COME
Member Since: July 15, 2006 Posts: 165 Comments: 52267
1242. marknmelb
8:38 PM GMT on August 01, 2006
Guess I need to start looking at what we have in the way of water, batteries, gas, and spam .. LOL
Member Since: July 17, 2006 Posts: 0 Comments: 406
1241. PascagoulaGal
8:32 PM GMT on August 01, 2006
Disasterworker. Thxs for ur hard work, its really appreciated. BUT hope u dont have to come see us anytime real soon. LOL. Stay safe.
1240. miracleaa1990
8:31 PM GMT on August 01, 2006
disasterworker - you an adjuster?
Member Since: August 1, 2006 Posts: 0 Comments: 284
1239. miracleaa1990
8:30 PM GMT on August 01, 2006
you guys are awesome...............where'd you all go?
Member Since: August 1, 2006 Posts: 0 Comments: 284
1238. disasterworker
8:29 PM GMT on August 01, 2006
Just started watching this site a few days ago. Have to thank everyone for their input, good or bad. It is really helping me understand how hurricanes form. Also help me plan for the next location I will be going to. LOL
Again, keep up the good work and maybe no one will need my assistance.
1237. kylejourdan2006
8:28 PM GMT on August 01, 2006
1990 - It's always better to be prepared than to get caught without any preparations. Watch until tomorrow evening then make your decision.
Member Since: July 18, 2006 Posts: 32 Comments: 1521
1236. miracleaa1990
8:26 PM GMT on August 01, 2006
ok you guys,
shall I prep, or what's this thing doing?
Member Since: August 1, 2006 Posts: 0 Comments: 284
1235. miracleaa1990
8:24 PM GMT on August 01, 2006
well, looks like i best put up the shutters for the season - I'm in Palm Beach,FL
Member Since: August 1, 2006 Posts: 0 Comments: 284
1234. Melagoo
8:23 PM GMT on August 01, 2006
This is an phenomenal weather website!

I have been to many and this site has it all.

Thank you Dr. Jeff Masters and the rest of the crew!
Member Since: July 31, 2006 Posts: 19 Comments: 1530
1233. Cavin Rawlins
8:20 PM GMT on August 01, 2006
NEW BLOG
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1232. Cavin Rawlins
8:18 PM GMT on August 01, 2006
saddle, you can say that....but what amazes me is how the place went from calm to gusty in minutes....Now the last time i was affected by a tropical system directly like Chris was Hurricane Lenny in 1999, so i forgot how it can be....
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1231. CrucianCrip
8:18 PM GMT on August 01, 2006
SJ..
The mods have lifted the 2k limit on blog comments.

CosmicEvents..

Am I doing my math wrong or are you really saying the storm could generate 500 mph winds (4800 knots)????
1230. quakeman55
8:17 PM GMT on August 01, 2006
So what's the consensus? How strong is it now?
Member Since: March 31, 2002 Posts: 1 Comments: 1276
1229. CosmicEvents
8:13 PM GMT on August 01, 2006
Well, it's been 18 hours since the first NHC discussion on TD3, and Chris has already intensified to twice what the wooses at the NHC predicted. At this rate of progression winds should be at about 1600 knots by the time it hits land, unless it goes into the GOM, then 4800 knots is possible. Unless of course it dissipates over Hispaniola or runs into unfavorable shear from the ULL's. We shall see.
Member Since: August 3, 2005 Posts: 10 Comments: 5459
1228. txweather
8:12 PM GMT on August 01, 2006
There won't be an eye for a while.
1225. txweather
8:10 PM GMT on August 01, 2006
Actually try a close up on the VIS. Right before the convection blew up yuo could almsot see the center get pulled into blob.

Also to help alittle some generalities on systems.

Td/early storm- burst of convection with just some organization

midstorm -ealyhurricane/strong storm-CDO, an area of strong convection forms near the center and persist with only alittle bandind.

Right now we are right at the border between these two and if the convection continue we will have a CDO.
1222. hurricaneman23
8:08 PM GMT on August 01, 2006
is south fla more in trouble now than before since it is moving nw. the track will have to me moved north slightly and south fla might be in the middle of the cone, you agree?
1221. Cavin Rawlins
8:08 PM GMT on August 01, 2006
saddle, yes...we have some very gusting winds now.....the sky is now almost completly cover.....it wont belong before we get some rain.....
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1220. CaneWatcher06
8:06 PM GMT on August 01, 2006
weather456 it could be a eye poping up but i dont no yet
1219. Cavin Rawlins
8:06 PM GMT on August 01, 2006
I dont believe it...but Chris might be on its way to become our first 'cane......
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1217. WSI
8:05 PM GMT on August 01, 2006
"Where does one find the latest computer models for Chris??"

Hey Jim. WU has some model runs here under their tropical section.

I also have a list of links on the Tropical Breakdown page at weathercore.com.
1215. mickeymouse8263
8:05 PM GMT on August 01, 2006
hello all, I live in Boca Raton and am watching this storm very closely, I just get this strange feeling about nasty storms and I am getting the same feeling I got when Francis, Jean and Wilma were approching. I hope I am wrong.
1214. Cavin Rawlins
8:05 PM GMT on August 01, 2006
3:45pm EDT-Convection continues to fire...Dr. Steve lyons said its strenghtening.....

I donot want to jump to conclusion, but someone tell if there is something forming under the recent convection....It looks pretty strange....



Member Since: July 24, 2005 Posts: 407 Comments: 19076
1213. txweather
8:05 PM GMT on August 01, 2006
thelmores, no offense intended.

Canewathcher06, unknown as of now, butt hat seems plausable. The bad thing about convection over the lcc is that I can't track it anymore. But before, it went under it almost looked like due w.
1211. Patrap
8:04 PM GMT on August 01, 2006
...Nasa scrubbed this mornings attempt to roll -out Atlantis to 39B due to Local weather concerns of T-storms in the 6-7 hr rollout window...have rescheduled for o200am est Wed morn..Launch Sched for Aug 27th...
Member Since: July 3, 2005 Posts: 415 Comments: 125628
1210. thelmores
8:04 PM GMT on August 01, 2006
i still say we will have hurr Chris by 11pm
Member Since: September 8, 2005 Posts: 0 Comments: 3788
1209. rxse7en
8:04 PM GMT on August 01, 2006
Has there ever been a case of Saharan dust knocking down a hurricane or a tropical storm for that matter?
Member Since: August 21, 2005 Posts: 0 Comments: 528
1206. earthlydragonfly
8:03 PM GMT on August 01, 2006
Is 99L the one ne of the bahamas? if so, I would say it is going from extratropical to tropical very soon. looks as if the thunderstorm activity is getting closer to the COC.
Member Since: July 1, 2005 Posts: 10 Comments: 1681
1205. ricderr
8:03 PM GMT on August 01, 2006
This blog knew about TD 03, 2 hours before the NHC had it....

Weather...correction This blog knew about TD 03, 2 hours before the NHC "reported it"..

NHC reports every 6 hours and updates every three when needed....funny..but one could get the impression here that they are the evil empire..more misinformation is passed on as fact here than they ever put out..but..this blog does make for better reading
Member Since: June 27, 2006 Posts: 668 Comments: 20163
1204. mahep1911
8:03 PM GMT on August 01, 2006
afternoon all how are we doing and how is our champ and where do we expect him to go i live in sw florida.
Member Since: July 17, 2005 Posts: 12 Comments: 793
1203. Cavin Rawlins
8:02 PM GMT on August 01, 2006
Starting to get a little breezy here......
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1202. txweather
8:02 PM GMT on August 01, 2006
hurricane23,good image thats the kind of picture I talked about.
1201. kylejourdan2006
8:02 PM GMT on August 01, 2006
Dr. Lyons says it is strengthening and we'll have a stronger storm at 5:00 PM.
Member Since: July 18, 2006 Posts: 32 Comments: 1521

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.