Hurricane Katia Part 2, TS Watch for Bermuda

[donsutherland1]

At 11 pm, Hurricane Katia was centered at 25.8°N 64.4°W. Over the past six hours, Katia has been tracking northwestward (323°).

Recent modeling has reduced the duration of any turn farther to the west. Given the close agreement between the 9/5 12z ECMWF, ECMWF ensembles, and both the 12z and 18z GFS, I have adjusted a portion of my track to the east. However, I continue to believe that the GFS probably has the best handle on the slower turn sharply to the east. Hence, I still expect Katia to cross 40N latitude to the west of 60W longitude.

My revised track estimate is:

30.0N 70.0W

35.0N 69.6W

40.0N 63.5W

Katia's rapid strengthening to Category 4 (135 mph maximum sustained winds) is consistent with the historic climatology associated with tropical cyclones that formed where Katia did. The historic climatology trumped the computer models when it came to intensity forecasting.

From August 29 (#226 in the first Katia thread), which references the statistics from historic climatology:

I took a further look at the region in which TD 12 developed, looking at all storms that formed in the vicinity of 7.4N-11.4N/21.3W-31.3W since 1950. 13/19 (68%) of storms grew into hurricanes. 11/13 (85%) of the hurricanes were major hurricanes. 9/13 (69%) of the hurricanes reached Category 4 or 5 with 4/13 (31%) reaching Category 5.

[Chicago Storm]

For those who have yet to see it... 24hr MIMIC loop (0z 5th- 0z 6th).

[Ginx snewx]

I always wonder the opposite-- why anyone here uses mph. When talking about tropical cyclones, the universal unit of wind-speed measurement in technical discussions is kt (or m/sec). Stuff like mph and kph are just for the general public-- like translating to baby talk for the average joe. This is is a technical forum, therefore kt makes sense.

Back to Katia... It's not the most attractive Cat 4 I've ever seen-- looks a bit smushed to me.

I like MPH, easy to relate. How many knots per hour does your car go?

[HurricaneJosh]

I like MPH, easy to relate. How many knots per hour does your car go?

Well, the beauty of "knot" is that it means "nautical miles per hour"-- so you don't have to say "knots per hour".

I think of my car's speed and wind speed as two unrelated things, honestly-- so I don't mind using different units of measurement for each.

I know I'm in the minority here, so I'll just hush up and slither back into my nerd nest.

[Ginx snewx]

Well, the beauty of "knot" is that it means "nautical miles per hour"-- so you don't have to say "knots per hour".

I think of my car's speed and wind speed as two unrelated things, honestly-- so I don't mind using different units of measurement for each.

I know I'm in the minority here, so I'll just hush up and slither back into my nerd nest.

Just joking, totally needs to be KTS especially for marine interests. Impressive storm, should be a nice Swell up here, water is so clean after Irene in RI, body surfing in my future.

[wxmx]

Knots is fine. I find kph easier to relate than mph, and probably most people outside of the US and Bermuda think the same, and I'm not complaining.

[phil882]

For those who have yet to see it... 24hr MIMIC loop (0z 5th- 0z 6th).

Nice loop... you can see how the storm,despite having a large eye never really shed the rain-bands around the circulation, and in the last few frames you see evidence that another EWRC is about to start. So no annular hurricane, despite my thoughts earlier today. I think the NHC might be making the right call here that Katia is peaking since I doubt the storm will have time to recover if another EWRC is starting now.

[Dino]

i think knots accounts for the curvature of the earth, so its the measure of speed traveled across an arc (which is more accurate). and mph is speed relative to the ground (ground could be inclined, steep, etc, but your speed will read x mph on that hill -- but that is not your "true" speed because since you're travelling 50mph up a hill, the hill means you're travelling a slightly longer distance, thus you're actually travelling slower than 50mph across the surface of the earth. i think.

[gymengineer]

i think knots accounts for the curvature of the earth, so its the measure of speed traveled across an arc (which is more accurate). and mph is speed relative to the ground (ground could be inclined, steep, etc, but your speed will read x mph on that hill -- but that is not your "true" speed because since you're travelling 50mph up a hill, the hill means you're travelling a slightly longer distance, thus you're actually travelling slower than 50mph across the surface of the earth. i think.

Uh... what you said cannot possibly be true since the knot-to-mph conversion stays constant throughout different topographies.

[friedmators]

i think knots accounts for the curvature of the earth, so its the measure of speed traveled across an arc (which is more accurate). and mph is speed relative to the ground (ground could be inclined, steep, etc, but your speed will read x mph on that hill -- but that is not your "true" speed because since you're travelling 50mph up a hill, the hill means you're travelling a slightly longer distance, thus you're actually travelling slower than 50mph across the surface of the earth. i think.

units of speed are all the same...some distance per some time.....your response actually scares me lol

[Dino]

units of speed are all the same...some distance per some time.....your response actually scares me lol

i thought wrong. nvm

[The Dude]

I always wonder the opposite-- why anyone here uses mph. When talking about tropical cyclones, the universal unit of wind-speed measurement in technical discussions is kt (or m/sec). Stuff like mph and kph are just for the general public-- like translating to baby talk for the average joe. This is is a technical forum, therefore kt makes sense.

Back to Katia... It's not the most attractive Cat 4 I've ever seen-- looks a bit smushed to me.

Agreed. We should always strive to use official technical terms here. Like, "smushed," for example...

[HurricaneJosh]

Agreed. We should always strive to use official technical terms here. Like, "smushed," for example...

[phil882]

Josh if you want to get "technical" most ATMS peer review literature now uses meters per second rather than knots. At least this has been the general shift in the past decade or so.

[ArtRosen]

Josh if you want to get "technical" most ATMS peer review literature now uses meters per second rather than knots. At least this has been the general shift in the past decade or so.

What about rotations per hour? How long does it take a point at 90 degrees to go completely 360 degrees around Katia? Do stronger hurricanes spin faster than weaker ones?

[Paweatherguy1]

I like MPH, easy to relate. How many knots per hour does your car go?

Honestly, I think sometimes people use knots, or when referring to cities on here, their airport call sign, simply to feel they know a little something more than the general public..

That is for a different discussion though.

[LocoAko]

What about rotations per hour? How long does it take a point at 90 degrees to go completely 360 degrees around Katia? Do stronger hurricanes spin faster than weaker ones?

I'd never even considered this, but what purpose would dictating wind speeds in terms of rotations per hour serve? The public understands that even less than the tangential velocities already given. It'd be odd. Plus I don't know that parcels, if you could even track them in this way, follow perfectly circular trajectories around storms (although I'm not 100% on this - Phil could probably elaborate).

[HurricaneJosh]

Josh if you want to get "technical" most ATMS peer review literature now uses meters per second rather than knots. At least this has been the general shift in the past decade or so.

I think you didn't read my post, as I specifically mentioned m/sec.

Technical discussions (NHC, BoM, etc.) are in kt. Academic papers-- at least the ones I read-- split down the middle between kt and m/sec. *All* reanalysis work is done in kt.

Honestly, I think sometimes people use knots, or when referring to cities on here, their airport call sign, simply to feel they know a little something more than the general public..

That is for a different discussion though.

Not really. If you do a lot of tropical-cyclone research, it's simply easier to use kt, as all NHC discussions and literature are in kt. I switched to kt fifteen years ago and it's just made everything so much simpler. Now I read and think in one unit of measurement only.

[phil882]

I think you didn't read my post, as I specifically mentioned m/sec.

Yep, I missed your first post on the matter, I just read the posts after that and tried to jump in... carry on

[jpeters3]

I'd never even considered this, but what purpose would dictating wind speeds in terms of rotations per hour serve? The public understands that even less than the tangential velocities already given.

Rotations per hour and tangential wind speeds will not be completely correlated. If we were to measure this rotations per hour at the distance away from the center where the fastest winds are: for a hypothetical hurricane with a 150 mph storm with a 30 mile wide eye, and assuming for the sake of argument that there is a ring ~20 miles from the center of the storm in the eyewall of 150 mph winds (even though in reality the fastest winds would only be in a small portion of the eye wall). The "eyewall" portion of the hurricane is rotating completely once every 50 minutes (.83 r/hr). For a storm with a 10 mile wide eye and ~ 10 mile ring, we have half the rotational velocity (.41 r/hr); however, both storms are the same intensity. The rotational speed really tells us nothing useful.

Plus I don't know that parcels, if you could even track them in this way, follow perfectly circular trajectories around storms (although I'm not 100% on this - Phil could probably elaborate).

They do not. The wind vectors are tilted inward.

[HurricaneJosh]

Yep, I missed your first post on the matter, I just read the posts after that and tried to jump in... carry on

Of the two, I prefer kt-- it just seems easier given that it's used operationally and in reports. But that's just my preference. I don't know anyone who's so hardcore that they work/think primarily in m/sec-- but I'm sure they're out there. You probably know a few.

[jpeters3]

*All* reanalysis work is done in kt.

all the reanalysis data i have seen is in m/s

From the NARR data i'm working with now:

6) vstm

units: m^2/s^2

long_name: 3-hourly V-component of Storm Motion

unpacked_valid_range: -75 75

precision: 2

actual_range: -44.45 50.61

missing_value: 32766

valid_range: -32766 -17765

add_offset: 252.65

scale_factor: 0.01

_FillValue: -32767

GRIB_name: VSTM

GRIB_id: 197

var_desc: V-component of Storm Motion

standard_name:

level_desc: 0-6000m above ground level

dataset: NARR 3-hourly

statistic: Individual Obs

parent_stat: Other

grid_mapping: Lambert_Conformal

coordinates: lat lon

weird, m^2/s^2?

[HurricaneJosh]

all the reanalysis data i have seen is in m/s

From the NARR data i'm working with now:

weird, m^2/s^2?

Huh? Go on the reanalysis site. All of the papers by Chris Landsea and his colleagues Re: historic storms are in kt, as are all of the best-track committee discussions. I know because I read them all like a nut.

[Paweatherguy1]

I think you didn't read my post, as I specifically mentioned m/sec.

Technical discussions (NHC, BoM, etc.) are in kt. Academic papers-- at least the ones I read-- split down the middle between kt and m/sec. *All* reanalysis work is done in kt.

Not really. If you do a lot of tropical-cyclone research, it's simply easier to use kt, as all NHC discussions are literature are in kt. I switched to kt fifteen years ago and it's just made everything so much simpler. Now I read and think in one unit of measurement only.

That's well and good, but for the general public, it will never fly. YOu would confuse the heck out of them. Even for me, as soon as I see knots, I go and convert it because I have a much better grasp is on what 115 MPH is than I do what 100 kts is...

[HurricaneJosh]

That's well and good, but for the general public, it will never fly. YOu would confuse the heck out of them. Even for me, as soon as I see knots, I go and convert it because I have a much better grasp is on what 115 MPH is than I do what 100 kts is...

No one here was suggesting kt for the general public.

I was saying that as a chaser and researcher and someone who is not "general public", kt works best for me.

[phil882]

Of the two, I prefer kt-- it just seems easier given that it's used operationally and in reports. But that's just my preference. I don't know anyone who's so hardcore that they work/think primarily in m/sec-- but I'm sure they're out there. You probably know a few.

Well I was told by my research adviser (Dr. Bosart) to do exactly that (think in m/sec) so I imagine he is one of em' There has also be a steadily increasing amount of literature that has made the conversion from knots to m/s although most of the time you see the two used interchangeably.

[ORH_wxman]

No one here was suggesting kt for the general public.

I was saying that as a chaser and researcher and someone who is not "general public", kt works best for me.

Knots is the way to go with anyone who is an invested tropical weenie. Very new tropical weenies will go mph, but very soon it should be knots.

Even as an icepu**y as you call me, I always go with knots on tropical systems. Its something that is learned over about 2 years IMHO for someone who is used to going by mph. TC's and knots are like bread and butter to me even though I'm not a TC expert.

[Paweatherguy1]

No one here was suggesting kt for the general public.

I was saying that as a chaser and researcher and someone who is not "general public", kt works best for me.

Ok, then I agree with you there.

[ORH_wxman]

Ok, then I agree with you there.

Learn knots with TCs...it will help a thousand-fold. Knots is everything we use at sea...and I think that is where the TC relationship with knots comes from. Its very useful to know the quick conversion in your head with knots and mph on these...but always refer to TCs as knots and you will never find yourself in trouble IMHO.

[HurricaneJosh]

Well I was told by my research adviser (Dr. Bosart) to do exactly that (think in m/sec) so I imagine he is one of em' There has also be a steadily increasing amount of literature that has made the conversion from knots to m/s although most of the time you see the two used interchangeably.

I figured you'd know such types. Since kt is used in all of the lit that's interesting to me (tropical cyclone reports, operational discussions, reanalysis papers, etc.), I'm stickin' with kt!

Knots is the way to go with anyone who is an invested tropical weenie. Very new tropical weenies will go mph, but very soon it should be knots.

Even as an icepu**y as you call me, I always go with knots on tropical systems. Its something that is learned over about 2 years IMHO for someone who is used to going by mph. TC's and knots are like bread and butter to me even though I'm not a TC expert.

Agreed-- it's a "language" that tropical nerds pick up with time.

P.S. I notice most severe/tornado literature is in mph, so I use mph when working in that arena. "When in Rome", I guess...

Ok, then I agree with you there.

Cool. And I agree with you-- the general public is not ready for kt.