CSU leaves their hurricane forecast unchanged; 92L and Colin's remains worth watching
Tropical Storm Colin was ripped apart by wind shear yesterday, and the storm's remnants are passing just north of the northernmost Lesser Antilles Islands today. Most of the heaviest thunderstorms are passing north of the islands, as seen on Guadeloupe radar. Long range radar out of Puerto Rico also shows this. Colin's remains are in a rather unfavorable environment for re-development, since the disturbance is passing beneath an upper-level low pressure system with dry air and high wind shear. Wind shear is a high 20 - 25 knots over Colin's remains this morning. Recent satellite imagery shows that heavy thunderstorm activity has increased in intensity and areal coverage over the past few hours, though, and Colin's remnants will need to be monitored for re-development.
Forecast for Colin's remains
The latest SHIPS model forecast predicts that wind shear will drop from 15 - 25 knots today to a moderate 15 - 20 knots on Thursday. Wind shear will continue to decline over the weekend, and this relaxation of shear prompts most of the major models to predict re-development of Colin sometime in the next four days. NHC is giving Colin's remain a 20% chance of developing into a tropical depression by Friday morning. A major trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough will pull Colin to the northwest and cause it to slow down. By Friday, Colin will be moving at half of its current speed. All of the major forecast models are predicting that the trough of low pressure will be strong enough to fully recurve Colin out to sea early next week. Colin's remains may pass close to Bermuda on Saturday, with the latest 06Z (2am EDT) run of the GFDL model predicting that Bermuda will experience tropical storm force winds on Saturday as Colin passes to the west of the island. The Hurricane Hunters are scheduled to investigate Colin's remains at 8pm EDT tonight. It currently appears that Colin will only be a threat to Bermuda and Canada.
Figure 1. Morning satellite image of Colin's remains and Invest 92L.
92L
A tropical wave (Invest 92) in the south-central Caribbean is moving west at 15 - 20 mph. This wave is over warm water and is experiencing low wind shear of 5 - 10 knots, and could show some development over the next two days. However, the wave's rapid westward motion should bring it ashore over Nicaragua and Honduras on Friday, or the Yucatan Peninsula on Saturday, and 92L probably does not have enough time over water to develop into a tropical depression. NHC is giving a 20% chance of this disturbance developing into a tropical depression by Friday morning. This storm was being tagged as 98L yesterday; I'm not sure why it is being called 92L today.
CSU's forecast numbers for the coming hurricane season remain unchanged
A very active Atlantic hurricane season is on tap for 2010, according to the seasonal hurricane forecast issued today, August 4, by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team continues to call for 18 named storms, 10 hurricanes, 5 intense hurricanes, and an Accumulated Cyclone Energy (ACE) index 185% of average. These are the same numbers as their June 2 forecast. Between 1950 - 2000, the average season had 10 named storms, 6 hurricanes, and 2 intense hurricanes. But since 1995, the beginning of an active hurricane period in the Atlantic, we've averaged 14 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast continues to call for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (50% chance, 31% chance is average) and the Gulf Coast (49% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also high, at 64% (42% is average.)
The forecasters cited four main reasons for an active season:
1) Moderate La Niña conditions should be present during the most active portion of this year's hurricane season (August - October). This should lead to reduced levels of vertical wind shear compared with what was witnessed in 2009.
2) Current SST anomalies are running at near-record warm levels. These very warm waters are associated with dynamic and thermodynamic factors that are very conducive for an active Atlantic hurricane season.
3) Very low sea level pressures prevailed during June and July over the tropical Atlantic. Weaker high pressure typically results in weaker trade winds that are commonly associated with more active hurricane seasons.
4) We are in the midst of a multi-decadal era of major hurricane activity, which began in 1995. Major hurricanes cause 80 - 85 percent of normalized hurricane damage.
Analogue years
The CSU team picked four previous years when atmospheric and oceanic conditions were similar to what we are seeing this summer. Those four years were 2005, the worst hurricane season of all time; 1998, which featured 3 major hurricanes, including Category 5 Hurricane Mitch; 1952, a relatively average year that featured just 7 named storms, but 3 major hurricanes; and 1958, a severe season with 5 major hurricanes. The mean activity for these five years was 17 named storms, 11 hurricanes, and 5 intense hurricanes, almost the same as the 2010 CSU forecast.
How accurate are the August forecasts?
The August forecasts by the CSU team over the past 12 years have had a skill 21% - 44% higher than a "no-skill" climatology forecast for number of named storms, hurricanes, intense hurricanes, and the ACE index (Figure 2). This is a good amount of skill for a seasonal forecast, and these August forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. This year's August forecast uses a new formula, so we don't have any history on how the technique has behaved in the past. An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.61 to 0.65 for their previous August forecasts using different techniques, which is respectable.
Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August), using the Mean Squared Error. The British firm Tropical Storm Risk (TSR) will issue their outlook for the 2010 Atlantic hurricane season on June 4. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) is scheduled to release their August forecast later today. NOAA will also be issuing their August forecast sometime in the next week.
This season has had three named storms so far (Alex, Bonnie, and Colin.) It will be difficult to have a season with 19 or more named storms, since the four seasons that had at least 19 named storms all had at least five named storms by this point (August 4.) These four seasons were 1887, 1933, 1995, and 2005.
Next update
I'll have an update on Thursday morning.
Jeff Masters
Reader Comments
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LOL, I have a more downcasted view of 92L and Colin.
Tropical Atlantic - Visible
Tropical Atlantic - Water Vapor
Tropical Atlantic - Funktop Color Infrared
Tropical Atlantic - Dvorak Infrared
be funny if colin ends up pulling a fast one and exits stage left
Would not be funny at all if it comes over my head in the process....
40-50 mph TS.
I saw that too, but I see the center more west than your mark. But, spin in animation looks weak like this is still an open wave, but a sharp one at that.
Too early to say. It will be slow to develop....which may allow it to get further west. It is still very much up in the air as to where it goes.
To early to tell atm.
the trough is going to be a dominant feature through the weekend and unless the nao become negative quicker than expected the trough will take this northwest and north. It is possible that it gets far north and then rishon begins building back in and it heads back west, however I am 95% certain that this will recurve and the other 5% is that it will hit am area from the Carolina northwards
The 60 mph TS readings where probably glitches. Flight level winds support a 40 mph TS.
Record breaking SST's bring record amounts of convection :-)
The CMC picked up on the CATL wave this morning and takes it north for a bit, before pushing it back W-WSW.
But that was the 12z and it's the CMC, so take that for what you will.
popcorn time hes going to ssurpise eveyone lol at dmax
the CMC track wise has been pretty good with these trop storms granted my sample size is bonnie and colin but still
No one has any data.
Probably an oil spill mission. I don't know.
If I remember correctly Nutria were brought to LA to breed for their fur.
I'm pretty sure it was good with Alex, too, but that was soooooo long ago, haha!
But Bermuda gets the right front quad from "colin" in that run, too... no good.
Does not seem like that is the case looking at shortwave IR loops.
Sorry, seem to be having some sort of quoting malfunction, anyway i would be watching closely
if i was their might not get to you though kinda looking more like between bahamas and US.
by looking at steering currents hope this storm doesnt get stupid!
thank you I was hoping someone who had more knowledge then me could shed some light. I appreciate it allstar.
i wish we could get that recon info
Nice update. Seems I am a Colin downcaster tonight. I don't believe the models about regneration right now, the ULL is too expansive (200 mb westerlies all the way to the Bahamas) and affecting Colin now, and sometimes models weaken ULLs too fast. I know Colin looks organized, but that's the upper portion of the storm. The lower portion is to the west of the organized clouds in the latest surface analysis, westerly shear from ULL in effect right now.
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