Hurricane Isaac, Part 3 - Analysis and Forecasting Thread

[Chaser25973]

Latest NHC guidance:

NHC says Isaac getting a little better organized. Pressure falls to 988 mb. Max winds remain 65 mph

[IsentropicLift]

I think it's important that we remember that Isaac is a large tropical cyclone, and in most cases the wind field will be slow to respond behind any significant pressure drops. While I think it's likely that Isaac will most likely undergoe a period of at least modest intensification over the next 24 hours, the surface winds may not respond in time for this to become a strong Hurricane intensity wise prior to landfall.

[Srain]

RECON data suggests that Isaac is still suffering from some southerly shear. The center appears elongated S to N and is not yet vertically stacked. The first visible imagery does suggest that Isaac is developing convection in the southern semi circle, but dry air to the E and S has kept development in check.

[lakeeffectkid383]

RECON data suggests that Isaac is still suffering from some southerly shear. The center appears elongated S to N and is not yet vertically stacked. The first visible imagery does suggest that Isaac is developing convection in the southern semi circle, but dry air to the E and S has kept development in check.

Ya WV is showing a good amount of dry air on the E and S side. Is that ULL to the SW of Isaac moving slower than expected thus keeping the dry air near him longer?

[Srain]

Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 27th day of the month at 13:03Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 25

Observation Number: 13

A. Time of Center Fix: 27th day of the month at 12:31:10Z

B. Center Fix Coordinates: 25°50'N 84°52'W (25.8333N 84.8667W)

B. Center Fix Location: 195 miles (313 km) to the WSW (254°) from Fort Myers, FL, USA.

C. Minimum Height at Standard Level: 1,342m (4,403ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 54kts (~ 62.1mph)

E. Location of the Estimated Maximum Surface Wind: 61 nautical miles (70 statute miles) to the SE (140°) of center fix

F. Maximum Flight Level Wind Inbound: From 199° at 40kts (From the SSW at ~ 46.0mph)

G. Location of Maximum Flight Level Wind Inbound: 94 nautical miles (108 statute miles) to the SE (130°) of center fix

H. Minimum Sea Level Pressure: 989mb (29.21 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,525m (5,003ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,523m (4,997ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 19°C (66°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Open, 09-24, RAGGED

M. Eye Shape & Diameter: Circular with a diameter of 32 nautical miles (37 statute miles)

N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature

N. Fix Level: 850mb

O. Navigation Fix Accuracy: 0.02 nautical miles

O. Meteorological Accuracy: 3 nautical miles

Remarks Section:

Maximum Flight Level Temp: 22°C (72°F) which was observed 12 nautical miles (14 statute miles) to the SSE (158°) from the flight level center

[dan11295]

Despite better radar presentation, pressure is virtually unchanged from last evening. clearly right now the ULL/dry air is enough of a hindrance to prevent any meaningful strengthening. models keep expecting it to move but I wonder if possibly it never does, which would likely result in a 75-80 mph cane at landfall. Not that we should not prepare for something stronger of course.

[40/70 Benchmark]

Despite better radar presentation, pressure is virtually unchanged from last evening. clearly right now the ULL/dry air is enough of a hindrance to prevent any meaningful strengthening. models keep expecting it to move but I wonder if possibly it never does, which would likely result in a 75-80 mph cane at landfall. Not that we should not prepare for something stronger of course.

I had a feeling this was going to have a tough time becoming more than a minimal cane.....one thing about these systems is that once they have an issue(s) plaguing them, it tends to be chronic, and too easily dismissed.

[heavy_wx]

The latest HRRR is suggesting that mid level dry air may be advected from the ULL over the Yucatan as well as from the southeast US into Isaac in the near term. SPC mesoanalysis and WV imagery confirms that there is an area of mid level dry air over the southeast with cyclonic flow around Isaac. This might prevent significant strengthening from occurring.

[Cory]

The 3km HRRR suggests some organization and strengthening by this evening (though it may have the same type of intensity bias as HWRF).

http://tinyurl.com/8sct6ly

[Cory]

The latest HRRR is suggesting that mid level dry air may be advected from the ULL over the Yucatan as well as from the southeast US into Isaac in the near term. SPC mesoanalysis and WV imagery confirms that there is an area of mid level dry air over the southeast with cyclonic flow around Isaac. This might prevent significant strengthening from occurring.

Funny we both posted about this model at the same time. Looking at its 10m wind field, it seems to want to tighten up the storm a little even with the dry air. I've never paid attention to how this model works with tropical systems, but it might be like HWRF where you can add dry air and 60 degree water and get a cat 2.

[heavy_wx]

Funny we both posted about this model at the same time. Looking at its 10m wind field, it seems to want to tighten up the storm a little even with the dry air. I've never paid attention to how this model works with tropical systems, but it might be like HWRF where you can add dry air and 60 degree water and get a cat 2.

I did notice that the HRRR brings the storm up to around 65-70 kts but based on the 1 km agl reflectivity, it keeps most of the convection to the west of the center longitude.

[wxmx]

I'm still on board for a possible cat 2. MW shows an incipient eyewall, which has at least 36 hours of gradual strengthening. Sat presentation shows an organizing cyclone also.

[Srain]

Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 27th day of the month at 13:48Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 25

Observation Number: 17

A. Time of Center Fix: 27th day of the month at 13:25:40Z

B. Center Fix Coordinates: 25°57'N 85°06'W (25.95N 85.1W)

B. Center Fix Location: 207 miles (332 km) to the WSW (257°) from Fort Myers, FL, USA.

C. Minimum Height at Standard Level: 1,346m (4,416ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 63kts (~ 72.5mph)

E. Location of the Estimated Maximum Surface Wind: 12 nautical miles (14 statute miles) to the W (274°) of center fix

F. Maximum Flight Level Wind Inbound: From 10° at 41kts (From the N at ~ 47.2mph)

G. Location of Maximum Flight Level Wind Inbound: 23 nautical miles (26 statute miles) to the W (271°) of center fix

H. Minimum Sea Level Pressure: 990mb (29.23 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 20°C (68°F) at a pressure alt. of 1,521m (4,990ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,525m (5,003ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 17°C (63°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character (Undecoded): RAGGED

M. Eye Shape & Diameter: Circular with a diameter of 26 nautical miles (30 statute miles)

N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature

N. Fix Level: 850mb

O. Navigation Fix Accuracy: 0.02 nautical miles

O. Meteorological Accuracy: 2 nautical miles

Remarks Section:

Maximum Flight Level Wind: 55kts (~ 63.3mph) in the northeast quadrant at 9:58:30Z

[40/70 Benchmark]

I'm still on board for a possible cat 2. MW shows an incipient eyewall, which has at least 36 hours of gradual strengthening. Sat presentation shows an organizing cyclone also.

If I had to toss out a LF #, then I'd say 80 mph.

[Weathergun]

The eye dropsonde reported on 8kt winds near the surface. So 990mb pressure in the last VDM, appears to be accurate.

^This is from the AF plane.

[Weathergun]

There is a NOAA plane in the Isaac too. Their VDM reports 989mb pressure. The dropsonde showed a 9kt surface wind:

Product: NOAA Vortex Message (URNT12 KWBC)

Transmitted: 27th day of the month at 13:56Z

Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 26

Observation Number: 32

A. Time of Center Fix: 27th day of the month at 13:15:30Z

B. Center Fix Coordinates: 25°58'N 85°02'W (25.9667N 85.0333W)

B. Center Fix Location: 202 miles (325 km) to the WSW (257°) from Fort Myers, FL, USA.

C. Minimum Height at Standard Level (Undecoded): NA NA

D. Estimated (by SFMR or visually) Maximum Surface Wind: 50kts (~ 57.5mph)

E. Location of the Estimated Maximum Surface Wind: 41 nautical miles (47 statute miles) to the NW (307°) of center fix

F. Maximum Flight Level Wind Inbound: From 39° at 53kts (From the NE at ~ 61.0mph)

G. Location of Maximum Flight Level Wind Inbound: 88 nautical miles (101 statute miles) to the NW (307°) of center fix

H. Minimum Sea Level Pressure: 989mb (29.21 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 16°C (61°F) at a pressure alt. of 2,467m (8,094ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 2,444m (8,018ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 11°C (52°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Not Available

M. Eye Shape: Not Available

N. Fix Determined By: Penetration

N. Fix Level: 700mb

Remarks Section:

Maximum Flight Level Wind: 56kts (~ 64.4mph) in the north quadrant at 8:53:05Z

[David Reimer]

There is a NOAA plane in the Isaac too. Their VDM reports 989mb pressure. The dropsonde showed a 9kt surface wind:

Product: NOAA Vortex Message (URNT12 KWBC)

Transmitted: 27th day of the month at 13:56Z

Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 26

Observation Number: 32

A. Time of Center Fix: 27th day of the month at 13:15:30Z

B. Center Fix Coordinates: 25°58'N 85°02'W (25.9667N 85.0333W)

B. Center Fix Location: 202 miles (325 km) to the WSW (257°) from Fort Myers, FL, USA.

C. Minimum Height at Standard Level (Undecoded): NA NA

D. Estimated (by SFMR or visually) Maximum Surface Wind: 50kts (~ 57.5mph)

E. Location of the Estimated Maximum Surface Wind: 41 nautical miles (47 statute miles) to the NW (307°) of center fix

F. Maximum Flight Level Wind Inbound: From 39° at 53kts (From the NE at ~ 61.0mph)

G. Location of Maximum Flight Level Wind Inbound: 88 nautical miles (101 statute miles) to the NW (307°) of center fix

H. Minimum Sea Level Pressure: 989mb (29.21 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 16°C (61°F) at a pressure alt. of 2,467m (8,094ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 18°C (64°F) at a pressure alt. of 2,444m (8,018ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 11°C (52°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Not Available

M. Eye Shape: Not Available

N. Fix Determined By: Penetration

N. Fix Level: 700mb

Remarks Section:

Maximum Flight Level Wind: 56kts (~ 64.4mph) in the north quadrant at 8:53:05Z

It looks like they have been having some minor communication issues with the vortex reports, but I can confirm it is 989 millibars. Using the standard reduction methods, that would be around 988 millibars. They're making another pass now.

[N. OF PIKE]

[LakeEffectKing]

FWIW

The 00z GFS/EnKF (experimental) individual members show a strong system at LF:

[Ed Lizard]

Mixed signals. Eyeballing anyway, CIMSS vort centers at 850, 700 and 500 mb aligned, shear is from South or Southeast about 10 knots. No really, really dry air to get pushed in by shear. Against development, MIMIC-TPW seems to have lost 60 mm TPW anywhere near Isaac, although I don't know if that is an artifact of the presentation. May not be based on few area soundings I can find. http://climate.cod.edu/flanis/raob_test.php?type=mex-20120827-12-skewt-MMUN-0 http://climate.cod.edu/flanis/raob_test.php?type=mex-20120808-12-skewt-MYNN-0

[LakeEffectKing]

And the 00z GFS/EnKF ensemble envelope:

[David Reimer]

Keep in mind that some of the higher resolution intensity models were showing Isaac taking its time getting together before rapidly ramping it up as it got closer to the coast. Now I'm not forecasting that to occur, but it would be unwise to discount the possibility yet. That isn't something I'm going to put out on my public feeds, but something I am watching closely.

[Derecho!]

Track seems to be curving more westwards based on the WC-130 VDMs.

Based on the extrap looks like it may be back down to 988 mb on the last pass, no sonde data yet.

[Connor McCrorey]

Finally some 50+ kt FL winds in the NW quadrant as recon is heading back out from the latest pass. With the slow pressure drop, large size of the system, and the fact that the center is moving into significantly deeper waters that should reduce any slight upwelling issues Isaac could be having, I still expect this to start strengthening a little more steadily any time now. I'm starting to feel like a broken record though, as it just hasn't happened yet. It does look to me like the shear is abating a bit. It's important to keep in mind that because of the fact that there is so much dry air to the SW of Isaac, the effects of this SWerly shear are going to be maximized. Once the shear gets below a certain threshold, I believe Isaac will take advantage of an environment that will be suddenly much improved.

[rcad1]

11 am pressure 988mb wind still 65 I think this thing looked better this morning than it does mow...

[David Reimer]

Product: NOAA Vortex Message (URNT12 KWBC)

Transmitted: 27th day of the month at 14:52Z

Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 26

Observation Number: 40

A. Time of Center Fix: 27th day of the month at 14:15:11Z

B. Center Fix Coordinates: 25°57'N 85°19'W (25.95N 85.3167W)

B. Center Fix Location: 220 miles (354 km) to the WSW (258°) from Fort Myers, FL, USA.

C. Minimum Height at Standard Level (Undecoded): NA NA

D. Estimated (by SFMR or visually) Maximum Surface Wind: 35kts (~ 40.3mph)

E. Location of the Estimated Maximum Surface Wind: 20 nautical miles (23 statute miles) to the E (97°) of center fix

F. Maximum Flight Level Wind Inbound: From 193° at 39kts (From the SSW at ~ 44.9mph)

G. Location of Maximum Flight Level Wind Inbound: 60 nautical miles (69 statute miles) to the ESE (122°) of center fix

H. Minimum Sea Level Pressure (Undecoded): 990 EXTRAP

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 16°C (61°F) at a pressure alt. of 2,448m (8,031ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye (Undecoded): 18 C / 2451

K. Dewpoint Temp (collected at same location as temp inside eye): 11°C (52°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Not Available

M. Eye Shape: Not Available

N. Fix Determined By: Penetration, Wind, Pressure and Temperature

N. Fix Level: Other - Not surface, 1500ft, 925mb (if vortex is newer than about mid 90's; see note for more), 850mb, 700mb, 500mb, 400mb, 300mb or 200mb

Remarks Section:

Maximum Flight Level Wind: 56kts (~ 64.4mph) in the north quadrant at 8:53:05Z

Maximum Flight Level Wind Outbound: 51kts (~ 58.7mph) in the north quadrant at 14:30:30Z

Maximum Flight Level Temp: 19°C (66°F) which was observed 19 nautical miles (22 statute miles) to the E (96°) from the flight level center

[Derecho!]

Supposedly uncontaminated 69 and 70 kt SFMR winds from AF Recon NW of the center....

[40/70 Benchmark]

Keep in mind that some of the higher resolution intensity models were showing Isaac taking its time getting together before rapidly ramping it up as it got closer to the coast. Now I'm not forecasting that to occur, but it would be unwise to discount the possibility yet. That isn't something I'm going to put out on my public feeds, but something I am watching closely.

IMHO, this caters to the point that we aren't going to have a very intense system...ie, a cat 1 cane.

Please correct me if I'm wrong, but how many systems do we see develop in a major cane over the shelf waters of the N GOM immediately prior to LF???

Again, I think a cat 2 is the realistic ceiling for this, with a cat 1 being much, much more likely.

[Connor McCrorey]

Time: 14:48:30Z

Coordinates: 26.3667N 85.8667W

Acft. Static Air Press: 842.6 mb (~ 24.88 inHg)

Acft. Geopotential Hgt: 1,463 meters (~ 4,800 feet)

Extrap. Sfc. Press: -

D-value: -

Flt. Lvl. Wind (30s): From 51° at 50 knots (From the NE at ~ 57.5 mph)

Air Temp: 16.1°C* (~ 61.0°F*)

Dew Pt: -*

Peak (10s) Flt. Lvl. Wind: 51 knots (~ 58.6 mph)

SFMR Peak (10s) Sfc. Wind: 65 knots (~ 74.8 mph)

SFMR Rain Rate: 49 mm/hr (~ 1.93 in/hr)

(*) Denotes suspect data

[David Reimer]

Supposedly uncontaminated 69 and 70 kt SFMR winds from AF Recon NW of the center....

True, but take a look at FL winds. They don't correlate well, so I'm pessimistic.

Peak (10s) Flt. Lvl. Wind:

51 knots (~ 58.6 mph)

SFMR Peak (10s) Sfc. Wind:

65 knots (~ 74.8 mph)