Hugh
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Bertha's forward motion hasn't decreased from what I can tell, if anything, it's moving faster, and maybe more north than west.
Regarding the pinhole eye, I've been thinking all day that Bertha was a borderline Cat 4 in the making, and now I think it's finally close to peaking in the early stages of an eyewall cycle.
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Hugh
Eloise (1975) - Elena and several other near misses (1985) - Erin & Opal (1995) - Ivan (2004)
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Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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Please be a little more cautious on your intensity forecasts - especially when rationale is not provided. Remember that 'gut feeling' forecasts belong in the Forecast Lounge.
Over the last 4 hours Bertha has continued to wobble along to the northwest (310 degrees) at 10 knots forward speed. IR imagery shows that the cloud tops have warmed slightly, so additional intensification of another 15 knots to reach Cat IV is not very likely. Modest upper level wind shear continues to impinge on the northwest quadrant of the hurricane - another factor against additional intensification in the short term.
ED
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Hugh
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NRL now shows winds up to 105kts, with pressure down to 952mb. That's actually a higher pressure than the 948 at the 5pm advisory, but at that point was showing 970mb with 90kt winds.
I know what you're saying about warming cloud tops, Ed, but I'm seeing some oscillation (for lack of a better term) in the tops, periodically warming but then cooling again. Bertha seems to be handling, and even beating off, the shear rather fiercely still.
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Hugh
Eloise (1975) - Elena and several other near misses (1985) - Erin & Opal (1995) - Ivan (2004)
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Robert
Weather Analyst
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Whats with that upper level low south of bermuda, sems once bertha really deppend she started heading right for the flow shooting around it.
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cieldumort
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Something which I should have made mention of a lot earlier. The upper level troffiness largely responsible for the increasing shear on Bertha from the northwest, has also been participating in enhancing the now very healthy outflow channel zoom-zooming off to her NE. So, there is some serious give and take going on over Bertha right now. On the one hand, you have the cyclone becoming (a little) asymmetric, as the shear starts to gnaw at her more. On the other, you still have this dynamite outflow. In fact, recently 's Dr. Lyons made mention that in his opinion, the outflow channel has been the largest single factor in the cyclone's intensification to a major hurricane, today.
It appears probable that Bertha has peaked out today at around 105 knots, give or take. This just about pushed the outer limits of Kerry Emanuel's Maximum Potential Intensity index (MPI), being that SSTs did not improve all that much over the course of just the past 18-24 hours.
Edited by cieldumort (Mon Jul 07 2008 10:17 PM)
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Hugh
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Quote:
It appears probable that Bertha has peaked out today at around 105 knots, give or take. This just about pushed the outer limits of Kerry Emanuel's Maximum Potential Intensity index (MPI), being that SSTs did not improve all that much over the course of just the past 18-24 hours.
Excellent point about SSTs, which makes the intensification all the more dramatic. I do believe you're correct in that Bertha has likely peaked at 105kts, but I don't believe I'd call the current presentation asymmetric exactly. The CORE of the hurricane, where the strongest convection is, is certainly tilted on its axis right now, but I've seen that before with hurricanes moving NW. What I'm most interested in, is the fact that Bertha is completely off the forecast track now.
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Hugh
Eloise (1975) - Elena and several other near misses (1985) - Erin & Opal (1995) - Ivan (2004)
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LoisCane
Veteran Storm Chaser
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Looking worse on by the minute...hour.
Which ever factor is causing the problem it is clear to see there is a lot going on.
http://www.ssd.noaa.gov/goes/flt/t1/bd-l.jpg
I wouldn't this is due to an .
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http://hurricaneharbor.blogspot.com/
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danielw
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AT 0300Z THE CENTER OF HURRICANE BERTHA WAS LOCATED NEAR LATITUDE
20.8 NORTH...LONGITUDE 52.8 WEST WITH MAXIMUM SUSTAINED WINDS NEAR
105 KTS...120 MPH...195 KM/HR.
HURRICANE BERTHA DISCUSSION NUMBER 20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
1100 PM EDT MON JUL 07 2008
DURING THE AFTERNOON HOURS BETWEEN 1900 AND 2300 UTC...BOTH AND
CIMSS OBJECTIVE T-NUMBERS WERE OSCILLATING AROUND 6.0 ON THE
SCALE. NORMALLY THESE NUMBERS CORRESPOND TO AN INTENSITY OF 115
KNOTS. DURING THAT TIME THE EYE BECAME VERY DISTINCT AND WAS
SURROUNDED BY VERY COLD TOPS. BERTHA COULD HAVE REACHED A PEAK
INTENSITY A LITTLE BIT HIGHER THAN PREVIOUSLY ESTIMATED DURING THAT
PERIOD. SINCE THEN...OBJECTIVE T-NUMBERS HAVE COME DOWN A LITTLE
BIT AND NEW ESTIMATES SUPPORT AN INTENSITY OF 105 KNOTS. MINIMUM
CENTRAL PRESSURE HAS ALSO BEEN ADJUSTED.
(spacing to permit easier reading and bold to highlight the Lois was speaking of.~danielw)
THE INTENSITY IS EXPECTED
TO BE CONTROLLED BY EYEWALL REPLACEMENT CYCLES DURING THE NEXT 12
TO 24 HOURS WHEN BERTHA COULD FLUCTUATE IN INTENSITY.
THEREAFTER...
THE OFFICIAL FORECAST CALLS FOR SLIGHT WEAKENING DUE TO INCREASING
SHEAR BUT NOT AS MUCH WEAKENING AS PREDICTED BY THE SHIPS MODEL.
NEVERTHELESS...THE INTENSITY FORECAST CONTINUES TO BE HIGHLY
UNCERTAIN...
Forecaster Avilla also added this to the 11PM Discussion. (Not that we needed a reminder~danielw)
BERTHA IS CERTAINLY NOT THE ONLY MAJOR HURRICANE THAT HAS FORMED IN
THE MONTH OF JULY. THE LAST OCCURRENCES WERE HURRICANES AND
EMILY IN 2005.
Edited by danielw (Mon Jul 07 2008 10:51 PM)
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LoisCane
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With almost any other storm i would agree however she is an extremely small, storm with hurricane force winds only 30 miles out from the eye and due to her size alone she is a small, strong pebble in a great big sea of weather and think her future intensity in the short term will be influenced by conditions around that small, seemingly intense core of category 3 winds.
I don't think her bad presentation on is due to eye wall replacement though it may be hard to determine without recon what is really going on from sats as they don't tell the whole story perfectly.
Her pressure has gone up steadily however they kept the winds at 120.
There is a lot going on there inside and around this storm. Would be fascinating to get a Gulfstream Jet in there and be able to after the fact figure out what happened here and use that data towards better intensity forecasts down the line.
http://cimss.ssec.wisc.edu/tropic/real-time/tpw2/natl/images/mosaic20080708T100000.gif
http://www.ssd.noaa.gov/goes/flt/t1/bd-l.jpg
Reminds me of a very small, intense Hurricane Bret that hit Texas
http://www.srh.noaa.gov/crp/docs/research/hurrhistory/bret/default.html
3rd paragraph down discusses Bret's size:
"An interesting meteorological phenomenon associated with Hurricane Bret, was the unusually small diameter of hurricane force winds that extended out from the center of this powerful storm. Even as Bret rapidly intensified to a major hurricane, the hurricane force winds (winds sustained of 75 mph or greater) extended out only 30 to 40 miles in all directions from the center."
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http://hurricaneharbor.blogspot.com/
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M.A.
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Bertha has had a very rough time today, it seems as if the shear has disrupted the the COC and even caused a bit of decoupling. The last frame of the sat loop is disturbing. The flare up of convection is right over the COC. I am wondering if the shear might be relaxing. I have not looked at the shear forecast today, so I can not speak informatively about it. It does appear that Bertha is far from done and might be making a bit of a come back as I type this.
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Hugh
Senior Storm Chaser
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Loc: Okaloosa County, Florida
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Two things I'm noticing tonight.
1. Bertha's making a bit of a comeback against the shear.
2. Bertha's moving more westerly than the official forecast.
I might be imaginng the movement, but the cloud tops have definately cooled once again, and convection has intensified.
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Hugh
Eloise (1975) - Elena and several other near misses (1985) - Erin & Opal (1995) - Ivan (2004)
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Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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Actually I think that you have made two good observations. The convective flareup appears to be to the south and southwest of the center, although pinpointing the center on IR imagery is always difficult. At 09/00Z I think that the center was around 23.0N 55.4W which would indicate more of a west northwest movement over the past three hours. Since the steering currents are quite weak, it could be just a temporary thing - or its also possible that the ridge to the north may have strengthen somewhat and the trough might have weakened somewhat. It will take a few more hours of observation. Also possible that the flareup itself nudged a slightly more westerly component to the track direction, but all the more reason why Bermuda needs to monitor Bertha's slow progress.
Cheers,
ED
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Hugh
Senior Storm Chaser
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The official forecast indicated that Bertha might start to wander around, but it mentioned it at day 4-5, not today... which is why the apparently shift in track surprised me a bit. Obviously you're right, it's too early to say it's a definate change in motion, but it's a bit disturbing nonetheless. If the ridge does indeed build back, that increases the uncertainty with Bertha, in my book.
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Hugh
Eloise (1975) - Elena and several other near misses (1985) - Erin & Opal (1995) - Ivan (2004)
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typhoon_tip
Meteorologist
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Quote:
Actually I think that you have made two good observations. The convective flareup appears to be to the south and southwest of the center, although pinpointing the center on IR imagery is always difficult. At 09/00Z I think that the center was around 23.0N 55.4W which would indicate more of a west northwest movement over the past three hours. Since the steering currents are quite weak, it could be just a temporary thing - or its also possible that the ridge to the north may have strengthen somewhat and the trough might have weakened somewhat. It will take a few more hours of observation. Also possible that the flareup itself nudged a slightly more westerly component to the track direction, but all the more reason why Bermuda needs to monitor Bertha's slow progress.
Cheers,
ED
Is it not true that track changes need 6 hours to confirm at the TPC? Am noticing that the 11pm discussion does not pick up on what seems to be a westward straddling of the 23rd parallel. I have also noticed a slowing of the forward motion. It does 'seem' upon satellite (IR, which as you said is difficult to use for these scenarios) that Bertha has resumed a more west motion. However, that could be 'optics' in that she burst convection somewhat, and the curl around the circulation makes the appearance of that west motion - though perhaps not really happening? Tough call.
John
Edited by typhoon_tip (Tue Jul 08 2008 11:31 PM)
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LoisCane
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It's more than a few frames. The movement is steady and what seems to be the center has moved past the forecast points.
I think she might be moving faster now but it's hard to tell especially since there seems to be discrepancy between forecasted movement and what the eye sees. Wish that recon had gone in or was going in... would provide more answers. In the past often recon would find subtle differences between what we thought we saw on sats and what was actually happening in the storm.
http://www.ssd.noaa.gov/goes/flt/t1/loop-ir2.html
Wanted to add that the models all show a much stronger storm almost from the get go and I keep thinking on a n older comment Ed made re: not handling the storm well the other day. The models all start with a storm much stronger than what we see and I would think that would make them somewhat suspect. I would like to see the models in the morning with current data to see if they truly reflect the storm as she is tonight and not how she was earlier in the day.
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http://hurricaneharbor.blogspot.com/
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LDH892
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You've all made some great points about Bertha's motion and intensity forecasting issues. Lois brings to light one problem that I've been thinking of as well, how most of these models aren't handling Bertha's intensity fluctuations at initiation very well. Another thing that has bothered me, which maybe someone else can explain further, is that over the past 2-3 days the official guidance has closely followed the CLIPER model. CLIPER is one of the lowest skilled models and for the official forecast and most of the model consensus to become aligned with the CLIPER seemed fishy to me, may just be this particular storm and its environment, or it may mean the models just haven't gotten a good grasp on Bertha (strength, size, motion, etc.). We'll see if the slight westward shift in the model consensus occurs in the 12Z run in the morning, perhaps the CLIPER will begin to be more of an outlier (like it should be), or perhaps since the steering currents will become so weak that model flip-flopping will become more of a normal occurrence (and the CLIPER may be the best choice - a.k.a climatology and persistence...). Enjoy reading everyones comments, thanks for any specific replies.
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typhoon_tip
Meteorologist
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Quote:
You've all made some great points about Bertha's motion and intensity forecasting issues. Lois brings to light one problem that I've been thinking of as well, how most of these models aren't handling Bertha's intensity fluctuations at initiation very well. Another thing that has bothered me, which maybe someone else can explain further, is that over the past 2-3 days the official guidance has closely followed the CLIPER model. CLIPER is one of the lowest skilled models and for the official forecast and most of the model consensus to become aligned with the CLIPER seemed fishy to me, may just be this particular storm and its environment, or it may mean the models just haven't gotten a good grasp on Bertha (strength, size, motion, etc.). We'll see if the slight westward shift in the model consensus occurs in the 12Z run in the morning, perhaps the CLIPER will begin to be more of an outlier (like it should be), or perhaps since the steering currents will become so weak that model flip-flopping will become more of a normal occurrence (and the CLIPER may be the best choice - a.k.a climatology and persistence...). Enjoy reading everyones comments, thanks for any specific replies.
I would like to comment on the Clipper model but unfortunately, can't. I do not normally use that tool; so I don't really have a handle on its known biases, thus, how to balance its solutions against the back-drop synoptics/other model solutions - which may and probably do have their own biases.
I will say that the TPC has intimated a couple of times that "meandering" was a concern in track guidance, for having weakening steering fields/intensity fluctuations. This seems reasonable and we are probably needing more time along these late evening behaviors, to determine how important they are.
Edited by typhoon_tip (Wed Jul 09 2008 12:29 AM)
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Robert
Weather Analyst
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Loc: Southeast, FL
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I thought i would share this from an old talk back when hurricane slowed down in shifty curents back in 2004 and started winding down. LIke berthat is doing now and forcast to do. Its from Hank Frank.
situation is becoming very complex. pressure has been essentially stable all day, but the expanding windfield and stall of the storm is throwing everything into ambiguity. if the storm spins down, the deep layer steering should kick in and take the system further west.. of course the models that forecast the system to up towards ga/sc a couple days ago were exhibiting a stall at times. associated shortwave ridge has stuck it's nose down into the nw caribbean and is contributing to it's own sheared situation.
i'm just not sure how the storm will respond to this.. as the storm spins down in a regime of conflicting steering.. there are lots of things that can happen.
HF 0114z04september
Edited by Robert (Wed Jul 09 2008 12:56 AM)
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Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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Normally will use a minimum of 6 hours for track forecast guidance (often more) and they do not like to make too significant a track change from one forecast to the next. Since persistence is the most reliable forecast tool in the tropics, this approach can usually work to your advantage - but not always. Case in point was Hurricane heading for Tampa when it was rather obvious that a remarkable late season summer front/trof was going to turn to the northeast.
The CLIPER has actually shown the best model performance on this storm - unusual, but it has. Except for poor intensity initialization, the has also done a good job with the track forecast. The 18Z run actually picked up on the current motion. The 00Z run is now coming in - - it places the storm near 25N 61.5W in 48 hours, then drifts it north for the next four days after that - with the system still below 30N six days from now. Bertha will probably still be around at this time next Wednesday.
Best guesstimate on position at 04Z was 23.0N 56.4W. Thats a motion due west at 12 knots over the past 4 hours and suggests that the ridge to the north has been reinforced.
Cheers,
ED
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WhitherWeather
Verified CFHC User
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Quote:
Best guesstimate on position at 04Z was 23.0N 56.4W. Thats a motion due west at 12 knots over the past 4 hours and suggests that the ridge to the north has been reinforced.
With all due respect to the six hour rule of thumb for persistence, still, taking the first and last images of the most recent loop and adding some orange reference lines for leading and bottom edges of the storm seems to give a visual nod to that "due west" assessment:
WhitherWeather
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WhitherWeather
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