Hurricane Isaac, Part 3 - Analysis and Forecasting Thread

[LakeEffectKing]

I don't know, there was one in Texas last time now there's 3. It does at least seem possible that this could leak off to the west despite most models suggesting a more northward turn during landfall.

As PSU pointed out, these are run off 06z data, and up until 12z this morning, the GFS had been trending westward...so it isn't the most up to date models to be looking at....more for research....and for us here on a BB....sheets and giggles...

[turtlehurricane]

Recon indicates that the wind fields have barely intensified near the core if any, most of the energy Isaac is producing is going towards strengthening the outer circulation, that's why we're still seeing 60 mph gusts in south Florida with feeder bands.

[salbers]

Pressure at Buoy 42003 is slightly falling or hovering at 985-986 mb, despite strong southerly winds and Isaac moving away from the site.

So at 10kt/mb reduction, we can call the central pressure now about 981mb?

[Ginx snewx]

Regarding surge, this is what the professionals whose job it is to project and interpret think.

http://w1.weather.gov/tcig/php/tcig_index.php?sid=lix&threat=coastal

[David Reimer]

70-74 Knot FL Winds

AF306 2709A ISAAC HDOB 28 20120827

194500 2556N 08619W 8420 01425 //// +174 //// 322034 036 035 004 01

194530 2555N 08620W 8404 01444 //// +175 //// 322035 037 037 006 01

194600 2554N 08621W 8410 01442 //// +170 //// 323034 035 043 007 01

194630 2552N 08623W 8407 01448 //// +167 //// 319033 035 044 007 01

194700 2551N 08624W 8412 01445 //// +173 //// 315036 037 050 011 01

194730 2550N 08625W 8419 01441 //// +160 //// 304042 049 056 016 01

194800 2549N 08626W 8399 01460 //// +157 //// 298048 049 058 021 01

194830 2548N 08627W 8413 01450 //// +152 //// 296054 058 058 022 01

194900 2547N 08628W 8407 01457 //// +154 //// 300061 063 056 019 01

194930 2546N 08629W 8414 01454 //// +154 //// 292059 060 058 014 01

195000 2545N 08631W 8415 01455 //// +152 //// 288062 065 058 013 01

195030 2544N 08631W 8403 01471 //// +161 //// 289060 065 057 012 01

195100 2543N 08633W 8419 01462 //// +168 //// 289061 064 056 009 01

195130 2542N 08634W 8403 01479 //// +171 //// 287066 069 054 008 01

195200 2541N 08635W 8411 01474 //// +170 //// 286072 073 053 007 01

195230 2540N 08635W 8421 01466 //// +179 //// 284073 074 051 006 01

195300 2539N 08636W 8405 01484 //// +181 //// 284072 072 050 005 01

195330 2538N 08637W 8413 01478 //// +185 //// 284070 072 048 006 01

195400 2537N 08638W 8408 01486 //// +181 //// 286071 072 050 006 01

195430 2536N 08639W 8413 01482 //// +174 //// 287069 070 048 007 01

$$

[turtlehurricane]

So at 10kt/mb reduction, we can call the central pressure now about 981mb?

If the buoy which has been getting battered by huge waves is still accurate, but I'm no expert on buoys. I'd stick with the recon pressure which is around 984 mb based on geopotential heights.

[EasternUSWX]

^{19:52:00Z 25.683N 86.583W 841.1 mb}

^{(~ 24.84 inHg) 1,474 meters}

^{(~ 4,836 feet) - - From 286° at 72 knots}

^{(From the WNW at ~ 82.8 mph) 17.0°C*}

^{(~ 62.6°F*) -* 73 knots}

^{(~ 83.9 mph) 53 knots}

^{(~ 60.9 mph) 7 mm/hr}

^{(~ 0.28 in/hr) 52.3 knots (~ 60.1 mph)}

^{Tropical Storm 72.6% 19:52:30Z 25.667N 86.583W 842.1 mb}

^{(~ 24.87 inHg) 1,466 meters}

^{(~ 4,810 feet) - - From 284° at 73 knots}

^{(From the WNW at ~ 83.9 mph) 17.9°C*}

^{(~ 64.2°F*) -* 74 knots}

^{(~ 85.1 mph) 51 knots}

^{(~ 58.6 mph) 6 mm/hr}

^{(~ 0.24 in/hr) 50.3 knots (~ 57.9 mph)}

^{Tropical Storm 68.9% 19:53:00Z 25.650N 86.600W 840.5 mb}

^{(~ 24.82 inHg) 1,484 meters}

^{(~ 4,869 feet) - - From 284° at 72 knots}

^{(From the WNW at ~ 82.8 mph) 18.1°C*}

^{(~ 64.6°F*) -* 72 knots}

^{(~ 82.8 mph) 50 knots}

^{(~ 57.5 mph) 5 mm/hr}

^{(~ 0.20 in/hr) 50.0 knots (~ 57.5 mph)}

^{Tropical Storm 69.4% 19:53:30Z 25.633N 86.617W 841.3 mb}

^{(~ 24.84 inHg) 1,478 meters}

^{(~ 4,849 feet) - - From 284° at 70 knots}

^{(From the WNW at ~ 80.5 mph) 18.5°C*}

^{(~ 65.3°F*) -* 72 knots}

^{(~ 82.8 mph) 48 knots}

^{(~ 55.2 mph) 6 mm/hr}

^{(~ 0.24 in/hr) 46.7 knots (~ 53.7 mph)}

^{Tropical Storm 66.7% 19:54:00Z 25.617N 86.633W 840.8 mb}

^{(~ 24.83 inHg) 1,486 meters}

^{(~ 4,875 feet) - - From 286° at 71 knots}

^{(From the WNW at ~ 81.6 mph) 18.1°C*}

^{(~ 64.6°F*) -* 72 knots}

^{(~ 82.8 mph) 50 knots}

^{(~ 57.5 mph) 6 mm/hr}

^{(~ 0.24 in/hr) 49.3 knots (~ 56.7 mph)}

^{Tropical Storm 69.4% 19:54:30Z 25.600N 86.650W 841.3 mb}

^{(~ 24.84 inHg) 1,482 meters}

^{(~ 4,862 feet) - - From 287° at 69 knots}

^{(From the WNW at ~ 79.3 mph) 17.4°C*}

^{(~ 63.3°F*) -* 70 knots}

^{(~ 80.5 mph) 48 knots}

^{(~ 55.2 mph) 7 mm/hr}

^{(~ 0.28 in/hr) 47.3 knots (~ 54.4 mph)}

^{Tropical Storm}

^{Actual strong FL winds. Could start the transfer down soon.}

[wxmeddler]

Holy SW Quadrant Batman.. 72 kt FL winds.

[ackwaves]

When you click on a 48 frame loop of the visible, it still seems the south side is being eroded perhaps...

http://weather.cod.edu/satrad/

[LakeEffectKing]

Recon indicates that the wind fields have barely intensified near the core if any, most of the energy Isaac is producing is going towards strengthening the outer circulation, that's why we're still seeing 60 mph gusts in south Florida with feeder bands.

The outside feeder bands over Florida are neutral to the storm, IMO.....i.e. they are neither adding nor subtracting from the COC strength....and that is modeled to be the case for another 6 hours or so....

The western bands surely are advecting vorticity into the COC along with latent heat....but can we get any EW to close off so we can increase the temp gradient from the center to the EW....

[A-L-E-K]

Holy SW Quadrant Batman.. 72 kt FL winds.

starting to see some improvement on the N/E sides but the W/S remains dominant.

[Superstorm93]

Pretty impressive FL winds.

Could support an upgrade.

Best 300mb signature I have seen with this system so far.

[David Reimer]

Dropsonde showed 982 millibars with 11 knot wind at splash, so looks like we're down to 981 millibars.

[EasternUSWX]

Clouds are thinning in center and on visible looks like might want to pop out soon. Also.

Information About Radiosonde:

- Launch Time: 19:36Z

- About Sonde: A descending radiosonde tracked automatically by satellite navigation with no solar or infrared correction.

Remarks Section...

Dropsonde Location: Dropped in eye.

Splash Location:

26.23N 85.94W

Splash Time:

19:38Z

Release Location:

26.22N 85.95W

View map

)

Release Time:

19:36:13Z

Splash Location:

26.22N 85.94W (

Splash Time:

19:37:31Z

Mean Boundary Level Wind (mean wind in the lowest 500 geopotential meters of the sounding):

- Wind Direction:

210° (from the SSW)

- Wind Speed:

14 knots (16 mph)

Deep Layer Mean Wind (average wind over the depth of the sounding):

- Wind Direction:

215° (from the SW)

- Wind Speed:

14 knots (16 mph)

- Depth of Sounding:

From 841mb to

982mb

[Superstorm93]

Down 3mb from the last pass.

Not bad.

H. 982 mb

I. 20 C / 1543 m

J. 22 C / 1544 m

K. NA / NA

L. OPEN N

M. C20

[lakeeffectkid383]

Should be good enough for an upgrade. Prob see 981mb with 75 mph winds at 5.

[LakeEffectKing]

So the last pass was 982.....pretty significant drop over the last bit...and would be lower than any model (except for the HWRF) has Isaac progged to be at this point.

[phil882]

Should be good enough for an upgrade. Prob see 981mb with 75 mph winds at 5.

We'll see... they didn't find any SFMR obs that supported hurricane intensity. I agree that this system is slowly strengthening, but it might not quite be there yet.

[turtlehurricane]

Dropsonde showed 982 millibars with 11 knot wind at splash, so looks like we're down to 981 millibars.

Guess that buoy was pretty accurate, NNE movement of the center too. Winds are probably good enough for the upgrade, finally.

[lakeeffectkid383]

We'll see... they didn't find any SFMR obs that supported hurricane intensity. I agree that this system is slowly strengthening, but it might not quite be there yet.

True but one would think that those 73kt FL winds should mix to the surface soon especally with pressures dropping. Should go up to at least 70mph at 5 , though I'm wondering if theyll upgrade it to hurricame status just because the public may take it a little more serious than a TS although were not exactly at the point of LF yet either. Time will tell.

[HKY_WX]

True but one would think that those 73kt FL winds should mix to the surface soon especally with pressures dropping. Should go up to at least 70mph at 5 , though I'm wondering if theyll upgrade it to hurricame status just because the public may take it a little more serious than a TS although were not exactly at the point of LF yet either. Time will tell.

Agreed. PR could lead to an upgrade. Honestly not a bad idea.

[phil882]

It is also interesting that they reported an eyewall of 20 nm that is open to the North. This almost fits perfectly with the HRRR forecast for around this time period. The remainder of the forecast shows the eyewall still taking time to get established, so I'd only expect slow intensification.

[Superstorm93]

Here is the HRRR aligned with what we have now.

(Only doing this since we don't have radar coverage)

[chris87]

it should be expected...it's a 90-minute forecast...it should look close to reality (assuming a proper, accurate initialization)...the same satellite images your eyes are ingesting were ingested by the HRRR...90 minutes isn't a lot of time to deviate from the initialization.

It is also interesting that they reported an eyewall of 20 nm that is open to the North. This almost fits perfectly with the HRRR forecast for around this time period. The remainder of the forecast shows the eyewall still taking time to get established, so I'd only expect slow intensification.

[lakeeffectkid383]

It is also interesting that they reported an eyewall of 20 nm that is open to the North. This almost fits perfectly with the HRRR forecast for around this time period. The remainder of the forecast shows the eyewall still taking time to get established, so I'd only expect slow intensification.

This model has been spot on for Isaac pretty much since it left Hati/Cuba. I like the way its performing and I would personally put alot of stock into this model for the remainder of Isaacs life considering its track record so far.Too bad it doesnt go out further.

[David Reimer]

It is starting to get that look you get with storms that are intensifying.

[HKY_WX]

It is also interesting that they reported an eyewall of 20 nm that is open to the North. This almost fits perfectly with the HRRR forecast for around this time period. The remainder of the forecast shows the eyewall still taking time to get established, so I'd only expect slow intensification.

http://rapidrefresh.noaa.gov/hrrrconus/jsloop.cgi?dsKeys=hrrr:&runTime=2012082717&plotName=1ref_t6sfc&fcstInc=60&numFcsts=16&model=hrrr&ptitle=HRRR%20Model%20Fields%20-%20Experimental&maxFcstLen=15&fcstStrLen=-1&resizePlot=1&domain=t6&wjet=1

link above is to the animation. it looks very nice by hour 15. it starts to take shape once it sheds that band to the NE over Florida/southeast.

[lakeeffectkid383]

http://rapidrefresh.noaa.gov/hrrrconus/jsloop.cgi?dsKeys=hrrr:&runTime=2012082717&plotName=1ref_t6sfc&fcstInc=60&numFcsts=16&model=hrrr&ptitle=HRRR%20Model%20Fields%20-%20Experimental&maxFcstLen=15&fcstStrLen=-1&resizePlot=1&domain=t6&wjet=1

link above is to the animation. it looks very nice by hour 15. it starts to take shape once it sheds that band to the NE over Florida/southeast.

I was thinking earlier that maybe that band over E Florida could be robbing some of the convection to the East of the center. That coupled with dry air. Hoping that once it sheds that band and we get D Max tonight it will finally get going better. As others have said it looks like an eye may trying to pop on visible with the thinning clouds but Im trying to determine if thats just dry air wrapping itself into the coc.

[EasternUSWX]

I was thinking earlier that maybe that band over E Florida could be robbing some of the convection to the East of the center. That coupled with dry air. Hoping that once it sheds that band and we get D Min tonight it will finally get going better. As others have said it looks like an eye may trying to pop on visible with the thinning clouds but Im trying to determine if thats just dry air wrapping itself into the coc.

You mean D Max not min. An recon has a eye open to the north so it is an eye trying to form.

[Superstorm93]

New HRRR run just coming in has some impressive 3-hr pressure falls later

http://rapidrefresh.noaa.gov/hrrrconus/from_jet/hrrr/t6/2012082718/pchg_t6sfc_f06.png