Global warming and the frequency of intense Atlantic hurricanes: model results

By: Dr. Jeff Masters , 1:37 PM GMT on April 05, 2010

Could global warming increase wind shear over the Atlantic, potentially leading to a decrease in the frequency of Atlantic hurricanes? There is a growing consensus among hurricane scientists that this is indeed quite possible. Two recent studies, by Zhao et al. (2009), "Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM", and by Knutson et al. (2008), "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", found that global warming might increase wind shear over the Atlantic by the end of the century, resulting in a decrease in the number of Atlantic hurricanes. For example, the second study took 18 relatively coarse (>60 km grid size) models used to formulate the 2007 IPCC climate report, and "downscaled" them using a higher-resolution (18 km grid size) model called ZETAC that was able to successfully simulate the frequencies of hurricanes over the past 50 years. When the 18 km ZETAC model was driven using the climate conditions we expect in 2100, as output by the 18 IPCC models, the authors found that a reduction of Atlantic tropical storms by 27% and hurricanes by 18% by the end of the century resulted. An important reason that their model predicted a decrease in the frequency of Atlantic hurricanes was due to a predicted increase in wind shear. As I explain in my wind shear tutorial, a large change of wind speed with height over a hurricane creates a shearing force that tends to tear the storm apart. The amount of wind shear is critical in determining whether a hurricane can form or survive.

Figure 1. Top: predicted change by 2100 in wind shear (in meters per second per degree C of warming--multiply by two to get mph) as predicted by summing the predictions of 18 climate models. Bottom: The number of models that predict the effect shown in the top image. The dots show the locations where tropical storms formed between 1981-2005. The box indicates a region of frequent hurricane formation where wind shear is not predicted to change much. Image credit: Geophysical Research Letters, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", by Vecchi and Soden, 2007.

Since the Knutson et al. study using the 18 km resolution ZETAC model was not detailed enough to look at what might happen to major Category 3 and stronger hurricanes, a new study using a higher resolution model was needed. This was done by a team of modelers led by Dr. Morris Bender of NOAA's GFDL laboratory, who published their results in Science in February. The authors used the GFDL hurricane model--the model that has been our best-performing operation hurricane track forecasting model over the past five years--to perform their study. The GFDL hurricane model runs at a resolution of 9 km, which is detailed enough to make accurate simulations of major hurricanes. The researchers did a double downscaling study, where they first took the forecast atmospheric and oceanic conditions at generated by the coarse (>60 km grid) IPCC models, used these data to initialize the finer resolution 18 km ZETAC model, then used the output from the ZETAC model to initialize the high-resolution GFDL hurricane model. The final results of this "double downscaling" study suggest that although the total number of hurricanes is expected to decrease by the end of the century, we should expect an increase of 81% in the number of Category 4 and 5 storms in the Atlantic. This trend should not be clearly detectable until about 60 years from now, given a scenario in which CO2 doubles by 2100. The authors say that their model predicts that there should already have been a 20% increase in the number of Category 4 and 5 storms since the 1940s, given the approximate 0.5°C warming of the tropical Atlantic during that period. This trend is too small to be detectable, given the high natural variability and the difficulty we've had accurately measuring the exact strength of intense hurricanes before the 1980s.The region of the Atlantic expected to see the greatest increase in Category 4 and 5 storms by the year 2100 is over the Bahama Islands (Figure 2), since wind shear is not expected to increase in this region, and sea surface temperatures and atmospheric instability are expected to increase there.

The net effect of a decrease in total number of hurricanes but an increase in the strongest hurricanes should cause an increase in U.S. hurricane damages of about 30% by the end of the century, the authors compute, assuming that hurricane damages behave as they did during the past century. Over the past century, Category 4 and 5 hurricanes made up only 6% of all U.S. landfalls, but accounted for 48% of all U.S. damage (if normalized to account for increases in U.S. population and wealth, Pielke et al., 2008.)

Figure 2. Expected change in Atlantic Category 4 and 5 hurricanes per decade expected by the year 2100, according to the Science paper by Bender et al. (2010).

Commentary
These results seem reasonable, since the models in question have been successfully been able to simulate the behavior of hurricanes over the past 50 years. However, the uncertainties are high and lot more research needs to be done before we can be confident of the results. Not all of the IPCC models predict an increase in wind shear over the tropical Atlantic by 2100, so the increase in Category 4 and 5 hurricanes could be much greater. Also, the GFDL model was observed to under-predict the strength of intense hurricanes in the current climate, so it may not be creating enough Category 4 and 5 hurricanes in the future climate of 2100. On the other hand, IPCC models such as the UKMO-HadCM3 predict a very large increase in wind shear, leading to a drastic reduction in all hurricanes in the Atlantic by 2100, including Category 4 and 5 storms. So Category 4 and 5 hurricane frequency could easily be much greater or much less than the 81% increase by 2100 found by Bender et al.

The estimates of a 30% increase in hurricane damages by 2100 may be considerably too low, since this estimate assumes that sea level rise will continue at the same pace as was observed in the 20th century. Sea level rise has accelerated since the 1990s, and it is likely that this century we will see much more than than the 7 inches of global sea level rise that was observed last century. Higher sea level rise rates will sharply increase the damages due to storm surge, which account for a large amount of the damage from intense Category 4 and 5 hurricanes.

Keep in mind that while a 30% in hurricane damage by the end of the century is significant, this will not be the main reason hurricane damages will increase this century. Hurricane damages are currently doubling every ten years, according to Pielke et al., 2008. This is primarily due to the increasing population along the coast and increased wealth of the population. The authors theorize that the Great Miami Hurricane of 1926, a Category 4 monster that made a direct hit on Miami Beach, would have caused about \$150 billion in damage had it hit in 2005. By 2015, the authors expect the same hurricane would do \$300 billion in damage. This number would increase to \$600 billion by 2025 (though I think it is likely that the recent recession may delay this damage total a few years into the future.) It is essential that we limit coastal development in vulnerable coastal areas, particularly along barrier islands, to reduce some of the astronomical price tags hurricanes are going to be causing. Adoption and enforcement of strict building standards is also a must.

The authors of the GFDL hurricane model study have put together a nice web page with links to the paper and some detailed non-technical explanations of the paper.

References
Bender et al., 2010, "Modeled Impact of Anthropogenic Warming on the Frequency of Intense Atlantic Hurricanes", Science, 22 January 2010: Vol. 327. no. 5964, pp. 454 - 458 DOI: 10.1126/science.1180568.

Vecchi, G.A., B.J. Soden, A.T. Wittenberg, I.M. Held, A. Leetmaa, and M.J. Harrison, 2006, "Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing", Nature, 441(7089), 73-76.

Vecchi, G.A., and B.J. Soden, 2007, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", Geophysical Research Letters, 34, L08702, doi:10.1029/2006GL028905, 2007.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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1255. SpicyAngel1072
 Sorry missed that post CycloneHi Storm!! How are you?
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1254. FloridaTigers
 Oz, I know you do your videos and chases for educational purposes, but of course there is a "thrill" aspect involved if one wants to chasing. Would you ever go chase a landfalling Category 5 storm?
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1253. WaterWitch11
 Quoting CycloneOz:No, we were on the highway headed to Artesia, but due west of the epicenter when it hit.\We had been underground at the caverns from 9am-5pm, though. Scary thought, especially when considering "Iceberg Rock.""The entrance is littered with large boulders that have fallen many years ago. These huge pieces of rock are astounding in size. The photograph to the right shows one such boulder. This boulder is called Iceberg Rock and weighs about 200,000 tons. If you can't imagine how big that is then think of this...it took 30 minutes to walk around it."i'm sure it was so much more amazing in person. i've been in the lava tubes in northern california that was pretty cool too.
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1249. Hurricanes101
 Quoting FloridaTigers:It doesn't have to be a major direct hit on Downtown Miami for the whole county to be affected. Miami's infrastructure was shut down completely by Andrew. Kendall is still part of Miami. I lived about 8 or so miles north of the eyewall and we still received more damage than I have ever seen from a hurricane, including any of the recent storms from 2005. Of course, I don't like at "being overdue" as a standard of anything. Be prepared for everything and anything no matter whatgreat point
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1248. tornadodude
 Severe Thunderstorm WarningSEVERE THUNDERSTORM WARNINGILC021-115-071945-/O.NEW.KILX.SV.W.0011.100407T1858Z-100407T1945Z/BULLETIN - IMMEDIATE BROADCAST REQUESTEDSEVERE THUNDERSTORM WARNINGNATIONAL WEATHER SERVICE LINCOLN IL158 PM CDT WED APR 7 2010THE NATIONAL WEATHER SERVICE IN LINCOLN HAS ISSUED A* SEVERE THUNDERSTORM WARNING FOR... NORTH CENTRAL CHRISTIAN COUNTY IN CENTRAL ILLINOIS... MACON COUNTY IN CENTRAL ILLINOIS...* UNTIL 245 PM CDT* AT 153 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED NEAR MOUNT AUBURN...OR 16 MILES NORTH OF TAYLORVILLE...AND MOVING NORTHEAST AT 45 MPH.* LOCATIONS IMPACTED INCLUDE... DECATUR...NIANTIC...HARRISTOWN...WARRENSBURG...FORSYTH...OREANA... MAROA...ARGENTA...BOODY...ELWIN...DECATUR AIRPORT AND OAKLEY.PRECAUTIONARY/PREPAREDNESS ACTIONS...SEVERE THUNDERSTORMS PRODUCE DAMAGING WIND IN EXCESS OF 60 MILES PERHOUR...DESTRUCTIVE HAIL...DEADLY LIGHTNING...AND VERY HEAVY RAIN. FORYOUR PROTECTION MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF YOURHOME OR BUSINESS. HEAVY RAINS FLOOD ROADS QUICKLY SO DO NOT DRIVEINTO AREAS WHERE WATER COVERS THE ROAD.&&A TORNADO WATCH REMAINS IN EFFECT UNTIL 700 PM CDT WEDNESDAY EVENINGFOR SOUTHEASTERN ILLINOIS.LAT...LON 3986 8877 3963 8926 3976 8935 3979 8929 3982 8926 3982 8924 3981 8923 3986 8922 4006 8895 4004 8878TIME...MOT...LOC 1858Z 235DEG 38KT 3979 8917WIND...HAIL 60MPH 1.00IN\$\$
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1247. Hurricanes101
 Quoting hydrus: Andrew did not make a direct hit on a major metro area and cause 100 billion dollars in damage. To me Andrew does count.Andrew absolutely counts, so really the S Florida area was the last in the US to be directly impacted by a Category 5, so I would say other coastlines are actually due before Florida.
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1245. stoormfury
 the way the scenario is now setting up inthe MDR it is possible the hurricane season could have an ealier start like the middle of may
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1244. FloridaTigers
 Quoting hydrus: Andrew did not make a direct hit on a major metro area and cause 100 billion dollars in damage. To me Andrew does count.It doesn't have to be a major direct hit on Downtown Miami for the whole county to be affected. Miami's infrastructure was shut down completely by Andrew. Kendall is still part of Miami. I lived about 8 or so miles north of the eyewall and we still received more damage than I have ever seen from a hurricane, including any of the recent storms from 2005. Of course, I don't like at "being overdue" as a standard of anything. Be prepared for everything and anything no matter what
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1243. sirmaelstrom
 № 1190Quoting twhcracker:.but if those who believe in GW are wrong, no harm done...I think you'll find not everyone agrees with the no harm done argument.
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1242. hydrus
 Quoting twhcracker:when i was a kid rowing up here on a bayou, we knew the hurricane was coming when the big roaches began to fly and buzz and dive bomb all over the house. I guess the humidity got to their insufficient little wings. Kind of a nasty way to get the bad news...lol
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1241. hydrus
 Quoting FloridaTigers:Wasn't Andrew our "due"? Andrew did not make a direct hit on a major metro area and cause 100 billion dollars in damage. To me Andrew does count.
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1240. CyclonicVoyage
 Quoting Hurricanes101:so is the rest of the US coastlinelets not pretend Florida is the only place that gets hit by hurricanes lolI'm not pretending actually. It's where I live and where I study. I don't know enough about other coastlines to make an accurate assumption.
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1239. 1900hurricane
 So far the only storm reports have been in the Medina area today, but I have a feeling that is about to change.
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1238. Patrap
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1237. indianrivguy
 Quoting jeffs713:I think if something like that happened, Florida would lose (temporarily) the moniker "The Sunshine State". It would be named something similar to one of our members here, "The Plywood State".more like the blue tarp stateI live right under that "72" in 1229
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1236. Hurricanes101
 Quoting CyclonicVoyage:Overdue actuallyso is the rest of the US coastlinelets not pretend Florida is the only place that gets hit by hurricanes lol
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1235. tornadodude
 Quoting Patrap:NEXRAD RadarSt. Louis, Echo Tops Range 124 NMI Max Tops were 43 K near St. Louisthey are beginning to blow up
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1234. Patrap
 NEXRAD RadarSt. Louis, Velocity Azimuth Display Wind Profile Range 124 NMI
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1233. Patrap
 NEXRAD RadarSt. Louis, Echo Tops Range 124 NMI Max Tops were 43 K near St. Louis
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1232. CyclonicVoyage
 Quoting FloridaTigers:Wasn't Andrew our "due"?If you live in Miami. Last storm to hit PBC was the Okeechobee hurricane.
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1231. jeffs713
 Quoting hydrus:It is getting too populated in Florida anyway. They say it will surpass New Yorks population in less than ten years. One day A hurricane similar to the 1926 storm will hit. Then the move to The Sunshine State will not look so appealing.I think if something like that happened, Florida would lose (temporarily) the moniker "The Sunshine State". It would be named something similar to one of our members here, "The Plywood State".
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1230. Patrap
 NEXRAD RadarSt. Louis, Storm Total Surface Rainfall Accumulation Range 124 NMI
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1229. CyclonicVoyage
 Overdue actually
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1228. tornadodude
 Quoting PcolaDan:thank yasomething to keep an eye on:
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1227. FloridaTigers
 Quoting CyclonicVoyage:Were due for that to happen.Wasn't Andrew our "due"?
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1226. Patrap
 Anytime tdude..big Storms there
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1225. CyclonicVoyage
 Quoting CyclonicVoyage:Were due for that to happen.We got a little scare from IKE. Next time might not be a scare.
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1224. PcolaDan
 Quoting tornadodude:can someone post a radar out of St Louis?there is a really nasty looking storm there
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1223. Patrap
 NOLA NWS Discussion As the trough moves east...remain positively titled...jet will shift to the front of the trough southwest to northeast over the middle Mississippi Valley to Great Lakes tonight. Sub-jet will push east over northwest Gulf...both jets creating a couplet over East Texas/western Louisiana this evening spreading east overnight. Model sounding showed slight veering but mostly speed shear and helicity values remain low below 100m/S. The convection will be linear with gusty winds being the main threat overnight. Precipitable water values will increase up to 1.5 inches along the trough axis toward midnight through 15z Thursday. Fast-moving system will result rainfall amounts between a half inch to an inch. In addition...cape values increase up to near 1500 j/kg before midnight across northwest zones and around 1000 j/kg area wide after midnight. Will try to confine higher chances of convection just ahead and around the frontal boundary around midnight for northwest zones to just before noon Thursday for Mississippi coast and coastal waters.
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1222. WaterWitch11
 Quoting CycloneOz:We were 20 miles away from a 4.3 magnitude earthquake on March 27. The epicenter was near Carlsbad, NM.What did we experience? Nothing at all.but you weren't underground
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1221. CyclonicVoyage
 Quoting hydrus: It is getting too populated in Florida anyway. They say it will surpass New Yorks population in less than ten years. One day A hurricane similar to the 1926 storm will hit. Then the move to The Sunshine State will not look so appealing.We're due for that to happen.
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1219. hydrus
 Quoting CyclonicVoyage:Man, Florida could get creamed this year. It is getting too populated in Florida anyway. They say it will surpass New Yorks population in less than ten years. One day A hurricane similar to the 1926 storm will hit. Then the move to The Sunshine State will not look so appealing.
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1218. Hurricanes101
 My numbers for this years hurricane season17 named storms10 hurricanes6 major hurricanesgoing to be an active season folks
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1217. tornadodude
 Quoting Patrap:thanks Pat
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1216. CyclonicVoyage
 Quoting SpicyAngel1072:Why ?Post 1178. If the forecast from the UK MET Office pans out for MSLP and 500mb Heights, it would tend to steer storms in that general direction. With areas in blue on the MSLP map being at highest risk.
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1215. tornadodude
 MESOSCALE DISCUSSION 0283 NWS STORM PREDICTION CENTER NORMAN OK 0129 PM CDT WED APR 07 2010 AREAS AFFECTED...NERN TX...SRN AND ERN AR WRN TN...AND EXTREME NWRN MS CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 071829Z - 072100Z STORM INTENSITIES WILL UNDERGO A GRADUAL INCREASE THIS AFTERNOON AND EVENING FROM NERN TX NRN LA...AR AND EVENTUALLY WRN TN. ISOLATED LARGE HAIL AND DAMAGING WIND ARE EXPECTED TO BE THE PRIMARY THREATS. AREA IS BEING MONITORED FOR A POSSIBLE WW. A COLD FRONT EXTENDS FROM A SURFACE LOW IN WRN IL SWWD THROUGH NWRN AR INTO NERN AND ERN TX. A MOIST AXIS WITH LOW 60S DEWPOINTS HAS ADVECTED NWD THROUGH PRE-FRONTAL WARM SECTOR...BUT BOUNDARY LAYER DESTABILIZATION HAS BEEN MODERATED BY WIDESPREAD LOW CLOUDS WITH SURFACE TEMPERATURES REMAINING IN THE LOW 70S. SPECIAL 18Z RAOB FROM LITTLE ROCK SHOWS MODEST LAPSE RATES AND AN INVERSION PRESENT JUST ABOVE 700 MB. HOWEVER...FORCING ALONG EWD MOVING BAROCLINIC ZONE AUGMENTED BY APPROACHING SHORTWAVE TROUGH WILL CONTINUE TO PROMOTE THUNDERSTORM DEVELOPMENT THE REMAINDER OF THIS AFTERNOON. LOW-LEVEL WIND PROFILES ARE UNIDIRECTIONAL...BUT DEEP SHEAR OF 40-50 KT WILL SUPPORT ORGANIZED STORM STRUCTURES INCLUDING SUPERCELLS AND BOWING LINE SEGMENTS. ..DIAL.. 04/07/2010 ATTN...WFO...MEG...JAN...LZK...SHV... LAT...LON 33159442 35719183 36399042 36148933 35018964 32529272 32199439 33159442
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1214. Patrap
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1213. twhcracker
 Quoting Chigz:Totally irrelevant post!!!but the one i responded to was relevant? i was just pointing out the non scientific-ness of it.
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1212. twhcracker
 when i was a kid rowing up here on a bayou, we knew the hurricane was coming when the big roaches began to fly and buzz and dive bomb all over the house. I guess the humidity got to their insufficient little wings.
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1211. Patrap
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1209. tornadodude
 can someone post a radar out of St Louis?there is a really nasty looking storm there
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1208. NttyGrtty
 I've lived in the FL panhandle for a very long time and I don't mess with hurricanes. Sure I'll joke that I don't even bring in lawn furniture for a cat 1 but at the cat 2/3 border, I'm outta here. Board up the house and pick a 3/4 day vacation spot. There was a graphic posted here the other day (by Pat I think) that showed Katrina 4 days out pointed at the panhandle so I picked what I thought at the time was a great 3/4 day vacation spot...NOLA! I cancelled the reservations the next day and ended up staying here as the predicted path moved west. It took 6 months to get the downtown Marriott to refund that first night's room that I never used. Long story to a long blog as we await the guest post...
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1207. hydrus
 Quoting AussieStorm:I agree with your numbers. I also hope we are both wrong. If those numbers come to fruition, There will definitely a couple of major landfalls. jmo
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1206. tornadodude
 As soon as I say it: SEL1 URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 61 NWS STORM PREDICTION CENTER NORMAN OK 125 PM CDT WED APR 7 2010 THE NWS STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF CENTRAL AND SOUTHERN ILLINOIS WESTERN AND NORTHERN INDIANA WESTERN KENTUCKY SOUTHEAST MISSOURI EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 125 PM UNTIL 700 PM CDT. TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS. THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 75 STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH NORTHWEST OF LAFAYETTE INDIANA TO 25 MILES EAST SOUTHEAST OF POPLAR BLUFF MISSOURI. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1). REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS. DISCUSSION...THUNDERSTORMS ARE INCREASING ALONG A SURFACE COLD FRONT OVER PORTIONS OF CENTRAL IL AND EASTERN MO. THESE STORMS ARE EXPECTED TO TRACK EASTWARD THIS AFTERNOON INTO PARTS OF WESTERN IND AND WESTERN KY. BREAKS IN THE CLOUDS AND RETURNING LOW LEVEL MOISTURE WILL PROVIDE SUFFICIENT INSTABILITY FOR A FEW SEVERE STORMS...WHILE FAVORABLE VERTICAL SHEAR PROFILES PROMOTE SUPERCELL/BOW STRUCTURES IN STORMS. LARGE HAIL IS THE MAIN THREAT...ALTHOUGH ISOLATED TORNADOES ARE ALSO POSSIBLE. AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM MOTION VECTOR 25030. ...HART
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1205. Chigz
 I am interested in the impacts on the central gulf coast this year...live in Houston!Lot of the MSLP, Precip analysis from UKMET spells bad news for the GULF!Anyone care to elaborate!? Thanks
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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