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 sammywammybamy:


And for the second time this season I have had a sat. picture of a poorly "organized" "system" appear under a spec of dirt on my monitor, and nearly made a pin-hole eye joke.
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Quoting Snowlover123:


Some slight divergance is also associated with 92L, though not as much as Colin.
Well the divergence associated with ex-Colin is caused by the TUTT.
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Something might be trying to get going just west of 30W above 10N in the Tropical Atlantic. The overshooting tops are becoming concentrated in that region and the cimss 850mb depicts a maxima around the aforementioned coordinates.
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Quoting wayfaringstranger:
Yeah, I am having a hard time imagining why this Colin hasnt been updated back to a TD at the least and possibly a TS


The Hurricane Hunters didn't find a closed COC.
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Jedkins- nice new avatar, can't hardly see the snakes tho cause of the t-shirt. Sigh...i can't believe you're all grown-up now.

ok, I read back, gotta coupla questions:

1. I don't see any rain coming for NE Fla from Colin. What am I missing?

2. Will I get any wave/ocean churning by Sunday from Colin on the NE Fla coast?

Thanks ya'll. :)
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I think that ex-colin is closed now... you can see it on vis... I wonder if they will reinitiate adv w/o recon or wait till recon gets there again
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Yeah, I am having a hard time imagining why this Colin hasnt been updated back to a TD at the least and possibly a TS
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Quoting MiamiHurricanes09:
Very strong divergence associated with ex-Colin, that should translate into lower surface pressures.



Some slight divergance is also associated with 92L, though not as much as Colin.
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Quoting angiest:


Neither was Colin. :) No closed circulation when he was named.
LOL, I'm sure that at some point they'll say that Alex didn't deserve hurricane status.

Enough of them now...back to the tropics.
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Quoting Levi32:


Probably will try to develop...could stay weak due to dry air, but we might get Danielle out of it, assuming 92L doesn't develop. It's even possible we could end up at the "E" storm before the week is out if 92L happens to develop, and boy would that hush up the downcasters for this season lol.

It would be like a switch with them.

Of course, the rest of us would just lean back and snicker.
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Quoting MiamiHurricanes09:
You wish. Even if we get to the "E" storm by the week's end they'll still be saying that September will be dead and that Bonnie shouldn't of been a tropical storm. LOL.


Neither was Colin. :) No closed circulation when he was named.
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Very strong divergence associated with ex-Colin, that should translate into lower surface pressures.

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Quoting TexasHurricane:
Levi, do you think 92L could make its way in the GOM?


I'm not Levi, but the model consensus doesn't think so, although some models take it into the extreme SW GOMEX.
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Quoting Levi32:


Probably will try to develop...could stay weak due to dry air, but we might get Danielle out of it, assuming 92L doesn't develop. It's even possible we could end up at the "E" storm before the week is out if 92L happens to develop, and boy would that hush up the downcasters for this season lol.


I Predict 20 Named Storms this Season.

3 Hurricanes
1 Major Hurricane
16 Tropical Storms
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Quoting unf97:


You can thank the penetration inland of the good ol' east coast seabreeze for generating those storms you received yesterday.


Yeah for sure, this is stuff I love around here! The weather is weird today though, all the convective cloud tops seem to be shredding apart today as they grow, it must be subsidence ahead of the weak trough in south Florida or something.
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Quoting Levi32:


Probably will try to develop...could stay weak due to dry air, but we might get Danielle out of it, assuming 92L doesn't develop. It's even possible we could end up at the "E" storm before the week is out, and boy would that hush up the downcasters for this season lol.
You wish. Even if we get to the "E" storm by the week's end they'll still be saying that September will be dead and that Bonnie shouldn't of been a tropical storm. LOL.
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Levi, do you think 92L could make its way in the GOM?
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694. Skyepony (Mod)
99E

rgb loop
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Quoting PRweathercenter:
Levi, there's a lot of talk of colin, what do you make of the wave that came off of africa?


Probably will try to develop...could stay weak due to dry air, but we might get Danielle out of it, assuming 92L doesn't develop. It's even possible we could end up at the "E" storm before the week is out if 92L happens to develop, and boy would that hush up the downcasters for this season lol.
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On the negative side, 92L is located in an area of negative lower level convergence- lower level divergence. Well see if the upper air high can cause enough divergence to induce forcing in the lower levels.
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Quoting aquak9:
(peeks around to make sure DocMaster's isn't posting)

OMG!!! The XTRAP has it headed straight towards me!!! AAAAHHHH!!!

(runs away, hits wall, knocks self out)


Haha! LMAO! :)
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Quoting Drakoen:
I appears that 92L has now become vertically stacked with an upper level high and the vorticity with the system is slowly increasing. It is going to need to start heading more poleward to avoid Nicaragua and for perhaps significant development to take place.
The last 3 ATCF center fixes suggest plain westward motion so it may just end up over central America. However models suggest that WNW motion should begin very soon.

AL, 92, 2010080406, , BEST, 0, 139N, 710W, 25, 1009, DB,
AL, 92, 2010080412, , BEST, 0, 140N, 724W, 25, 1009, DB,
AL, 92, 2010080418, , BEST, 0, 140N, 739W, 25, 1009, DB,
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Quoting xCat6Hurricane:


Hurricane Danielle.


No that's Earl. :P
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(peeks around to make sure DocMaster's isn't posting)

OMG!!! The XTRAP has it headed straight towards me!!! AAAAHHHH!!!

(runs away, hits wall, knocks self out)
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Quoting PRweathercenter:
Levi, there's a lot of talk of colin, what do you make of the wave that came off of africa?


Hurricane Danielle.
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Quoting Levi32:


Oh yeah there's banding, and I don't think there is any "window" for strengthening....it simply gets better and better as time goes on.
Levi, there's a lot of talk of colin, what do you make of the wave that came off of africa?
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I appears that 92L has now become vertically stacked with an upper level high and the vorticity with the system is slowly increasing. It is going to need to start heading more poleward to avoid Nicaragua and for perhaps significant development to take place.
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Quoting hurricanehunter27:
Edit Failed!
I was actully looking at comment 617 much closer sat pic.

I was just joking around.
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Quoting Jax82:
When is the MJO expected to be in the upward phase in Octants 1/2?


Klotzbach's thinking on the MJO Link


The Madden-Julian Oscillation is currently weakening over the longitude of Indonesia (Figure 3). Both the statistical models as well as the dynamical models tend to indicate that the MJO should continue to weaken over the next several days. The ensemble Global Forecast System (GFS) is predicting the MJO to remain of weak magnitude in week one with a potential redevelopment of the MJO in the Indian Ocean in week two (Figure 4). Typically, when the MJO is located over the Indian Ocean (Phases 1 and 2), TC activity in the Atlantic is enhanced (Table 2).
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The circulation just northeast of Puerto Rico represents where Colin wanted to go today but got denied. That circulation is hindering development of the one to the east, but once it gets out of there we should see the real center tighten up nicely. It's already tightening a lot in at least the mid-levels.
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Quoting unf97:


You can thank the good ol' east coast seabreeze for generating those storms you received yesterday.


And today; here in Bonita Springs (between Fort Myers and Naples), we've had non-stop lightning and rain for the better part of an hour. Nice...

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Quoting hurricanehunter27:


I was actully looking at comment 617 much closer sat pic.
He/she was messing around. Only strong tropical storms or hurricanes acquire eyes.
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678. unf97
Quoting Jedkins01:


We got absolutely wacked last few days on the west coast of Florida, very powerful thunderstorms, actually had 3 rounds yesterday! Yesterday we had 4.02 and just astounding lightning, a whole lot of wind as well!


You can thank the penetration inland of the good ol' east coast seabreeze for generating those storms you received yesterday.
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677. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting angiest:
656 - I can't see the eye. Must be a pin-hole!


I was actully looking at comment 617 much closer sat pic.
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Quoting MiamiHurricanes09:
According to this the circulation of ex-Colin is only under 5-10 knots of wind shear while the northern quadrant of the system is under 20 knots wind shear.



Check out the anti-cyclone over 92L.
Member Since: July 8, 2005 Posts: 259 Comments: 24167
Quoting sammywammybamy:


Levi,

If you can Read this:

I Belive i can see banding in the images of collin.

That 52mph wind was not contaminated.

Stormw , says their is a window for strengthing at 8pm.

What do u think?


Oh yeah there's banding, and I don't think there is any "window" for strengthening....it simply gets better and better as time goes on.
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According to this the circulation of ex-Colin is only under 5-10 knots of wind shear while the northern quadrant of the system is under 20 knots wind shear.

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92L taking an Alex path or something similar?
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special wx advisory for Bonita springs FL///


NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATES STRONG THUNDERSTORMS
LOCATED NEAR BONITA SPRINGS...MOVING WEST AT 5 MPH. THESE STORMS
WILL AFFECT ESTERO...BONITA SPRINGS...AND BONITA SHORES...UNTIL 445
PM EDT.

GUSTY WINDS 35 TO 45 MPH WILL BE POSSIBLE. FREQUENT LIGHTNING IS
EXPECTED. TO BE SAFE GO INDOORS IMMEDIATELY. IF CAUGHT
OUTSIDE...FIND A LOW SPOT...AND STAY AWAY FROM TALL OBJECTS.
TORRENTIAL RAINS WILL REDUCE VISIBILITY TO NEAR ZERO AND WILL CAUSE
PONDING OF WATER ON ROADWAYS. MOTORISTS TRAVELING ALONG I 75 BETWEEN
BONITA SPRINGS AND ESTERO SHOULD EXERCISE EXTREME CAUTION.
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ULL and dry air are causing issues on the west side
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656 - I can't see the eye. Must be a pin-hole!
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It will be interesting to see how this changes moving forwrd

Click to enlarge and lengthen the run



Member Since: June 12, 2005 Posts: 6 Comments: 8186
Looks like outflow on the west side is getting suppressed. Is that from the ULL or dry air or both? That seems like it's hindering development although it's re-firing convection around the center. Persistent little system...
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Yes Colin is going a LOT slower than it was.
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Quoting Jeff9641:


I am seeing this on the models this afternoon. It looks if finally E C FL and NE FL will see some substantial rain. This could be the start of very wet few months across FL.


We got absolutely wacked last few days on the west coast of Florida, very powerful thunderstorms, actually had 3 rounds yesterday! Yesterday we had 4.02 and just astounding lightning, a whole lot of wind as well!
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662. 7544
does anyone know if colin in slowing down in spped tia looks like he is here
Member Since: May 6, 2007 Posts: 0 Comments: 6855

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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.

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