CSU leaves their hurricane forecast unchanged; 92L and Colin's remains worth watching

By: Dr. Jeff Masters , 2:38 PM GMT on August 04, 2010

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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

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Quoting MiamiHurricanes09:
More like T2.0. At least this time they don't have to base the advisory off of the satellite estimate but rather what Recon finds.


Well it is important to keep in mind organization matters also when it comes to classifying systems. A closed circulation with a T1.0 system would mean nothing. At least were looking at T1.5 and 2.0 now.
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GFS is running!
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Quoting calder:


which aren't at TS level... They wont classify until the HH find a closed low


The Hurricane Hunters found Tropical Storm winds, and mentioned them in their discussion.

HOWEVER...
THE AIRCRAFT FOUND WINDS OF TROPICAL-STORM FORCE IN THE
NORTHEASTERN PORTION OF THE SYSTEM.


If this has indeed a Closed Circulation, which according to satellite imagery, it does, then we now have our Colin back with us again.
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1009. will45
if it has slowed down that would lead to a better developed system and would be easier for it to close the circulation
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Quoting xcool:


Nice ball of convection.

Ex-Colin: I'm a big kid now!!!
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Cloud pattern is still elongated north-south
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Quoting extreme236:
NHC may wanna see a T number of 2.5 before they classify this a TS again.
More like T2.0. At least this time they don't have to base the advisory off of the satellite estimate but rather what Recon finds.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting extreme236:


I'm fairly certain they do updates as they are warranted. You may not see a renumber but the timestamp will be different if there was an update.


Yeah I suppose. All of the updates in the individual storm files end in 00, 06, 12, 18, but a lot of times they edit the coordinates or other info without changing that, although the timestamp change is reflected on the general tcweb folder.
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1003. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15670
Quoting Snowlover123:


This shear map tends to disagree with your statement.



Currently it's under about 10-20 kts. of shear, which is NOT condusive for rapid stregnthening.

http://cimss.ssec.wisc.edu/tropic2/real-time/windgridmain.php?&basin=atlantic&sat=wg8




and that shear map could be a little off
Member Since: May 21, 2006 Posts: 5091 Comments: 115074
Quoting cg2916:


Storm, Miami, Levi, your thoughts?
Recon will be investigating ex-Colin at 00z. If they do find a closed surface circulation it is very likely that we will get T.S Colin back. My chance that ex-Colin will regenerate into Colin in the next 48 hours is high (60%).
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting belizeit:
It looks like Colin has almost stalled which will allow it to strengthen rapidly


This shear map tends to disagree with your statement.



Currently it's under about 10-20 kts. of shear, which is NOT condusive for rapid stregnthening.

http://cimss.ssec.wisc.edu/tropic2/real-time/windgridmain.php?&basin=atlantic&sat=wg8
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Quoting Snowlover123:


Perhaps DVORAK T NUMBERS. Did you use that, Sammy?


which aren't at TS level... They wont classify until the HH find a closed low
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Quoting jasoncoolman2010xx:
MAYBE INVEST 94L down the road



we have not even seen 93L yet
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994. xcool
moving very slowly
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Quoting sammywammybamy:
This is a Ts:



It looks pretty impressive in this picture.
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Colin is not moving at a fast clip anymore. In fact, I think the movement is a slow west. The trough is lifting out, and moisture is ever expanding to his west. It will be interesting to see if Colin slips under the lifting low...
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Quoting hurricanehunter27:
Looks like TS colin is back :D
It looks better then before.
Beacuse it is better than before!
It looks like Colin has almost stalled which will allow it to strengthen rapidly
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NHC may wanna see a T number of 2.5 before they classify this a TS again.
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Quoting calder:


based on what?


Perhaps DVORAK T NUMBERS. Did you use that, Sammy?
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987. xcool
Colin strong Little boyz
Member Since: September 26, 2009 Posts: 2 Comments: 15670
Quoting sammywammybamy:
This is a Ts:



Good Evening! Nice satellite imagery, Colin! Whoah. I would be VERY surprised if the NHC does not classify this as at least a Tropical Depression, before the day is over.
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Quoting sammywammybamy:
This is a Ts:



based on what?
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ex Colin I think is now Colin again
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Looks like TS colin is back :D
It looks better then before.
Beacuse it is better than before!
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982. xcool
poof 97e
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981. 786
Finally some good rain and some thunder from 92Ls rain band
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Quoting Tazmanian:
97E and 99E is RIP


99E is certainly not rip.
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04L/XX/XL
MARK
20.11N/62.66W
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97E and 99E is RIP
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Quoting Hurricanes101:
961. SeniorPoppy 9:34 PM GMT on August 04, 2010

Exactly my point, which is why I reacted in the first place to the comment you commented on; I think some come on here just to pick a fight or something lol, maybe it makes them feel important


I'll admit, I went over the top yesterday with some of my comments. Everyone is entitled to their opinion. :)
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the navy site never dropped the 04 even tho it was downgraded
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974. 7544
looks like 45 to 50 ts here
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Quoting HurricaneSwirl:


Well, that was at 2PM EDT, and the ATCF site doesn't update until 8-8:30, does the ATCF do special updates like the NHC does? I don't think they do, unless you count renumbers and activations I think they do those whenever they want.. but we won't get a renumber to 04L because the data is already being kept in a file named invest_al042010.invest. So I'm not sure.


I'm fairly certain they do updates as they are warranted. You may not see a renumber but the timestamp will be different if there was an update.
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Not that it matters, but CSU is now calling it a Tropical Storm, where a few hours ago they had it listed as a TD.
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Quoting BaltOCane:
does anyone check out stormpulse.com?

I ask only because they have 92L's location at 12.8N 76.6W while the WU site has it at 14.0N 73.9W... as of 2pm EDT

and that's kind of a big difference...
comments?
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961. SeniorPoppy 9:34 PM GMT on August 04, 2010

Exactly my point, which is why I reacted in the first place to the comment you commented on; I think some come on here just to pick a fight or something lol, maybe it makes them feel important
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967. 7544
Quoting extreme236:


Agreed. Maybe at 11 we might see a regenerated Colin but not yet.


if its on the navy site as a ts again the nhc will make a speacial statement or will up it on the 8pm thats right but being its getting close to some one we just might get the update speacial state before the 8pm imo
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Quoting extreme236:


Not on the ATCF site. It still says WV. So no TS Colin yet.


Well, that was at 2PM EDT, and the ATCF site doesn't update until 8-8:30, does the ATCF do special updates like the NHC does? I don't think they do, unless you count renumbers and activations I think they do those whenever they want.. but we won't get a renumber to 04L because the data is already being kept in a file named invest_al042010.invest. So I'm not sure.
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It will certainly be interesting to see what the next TWO says, maybe something like: Hurricane Hunters are currently observing the remnants of Colin to see if we have a closed circulation, there is a high chance, 70% of redevelopment of Colin in the next 48 hours.
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964. bwi
92l looks to my untrained eyes like it might have some curved cloud structure developing, around the area of 14-15n and 75-76w. I'll be interested to see if that area flares back up tonight.
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also the NHC may also hold to regenerate colin to see if convection holds too
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Quoting Seflhurricane:
too much windshear maybe friday what i want to see is the models on the new center


An anti-cyclone has developed over the system, so wind shear is actually on the way down. However, the anticyclone could fall apart and allow Colin to be sheared again. Hard to say. Like I said, trends need to continue. They won't re-designate Colin until the hunters investigate.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.