Erin NHC Report is up (Read it on page 3)

[Wthrman13]

I was rather disappointed in the tropical cyclone report, and not just because I feel that Erin was indeed a tropical cyclone over OK. I was expecting a more detailed look at the possible mechanisms for intensification, not just a vague sentence speculating on the influence of an upper-level shortwave trough (which "legit" TC's over water are hardly immune from, anyway). What about the low-level jet? What about the very moist pre-existing surface conditions? The truth is, I don't know what effect these and other factors had on Erin's regeneration, which is why I was looking forward to NHC's take on them.

Fortunately, the story will not end here. This is such an interesting case that I'm sure not a few researchers (perhaps even myself some day, when I have time) will study this event in an effort to better explain it.

In regards to the eye-like feature, it lasted for several hours (coming and going, not necessarily continuous) and was accompanied by a well-defined large-scale intense velocity couplet on radar. It was also co-located with a well-defined surface low-pressure center, and the strongest surface winds were found nearby. This was hardly circumstantial radar structure that just "looks" like an eye.

As for myself, I was in Norman at the time and got to experience hours of heavy thunderstorms with very warm, gusty winds out of the south in one of the outer rainbands. I've been in two hurricanes, and the first thing I thought of when the storm first woke me up that night, before I even had a look at the radar, was how much this reminded me of my hurricane intercepts, and not in the slightest of outflow winds from a typical MCS.

[Tampa Bay Hurricane]

Now that a professional meteorologist thinks this may have been more
tropical like, I can safely say I think this was a tropical storm, and
depending on what the highest wind was I am willing to classify it
a strong tropical storm or higher.

[MiamiensisWx]

Originally, I strongly agreed that Erin was a TS or STS over the state until recent research revealed new information. I recently consulted another board, and a meteorologist mentioned Erin actually featured a weak cold core over Oklahoma, which may have been a primary factor the TPC's "remnant low" classification (in addition to the data in the TCR) over the state. If a warm core was present, I would have maintained my original stance.

If this is correct, Erin was NOT a TS or STS over the state.

[Squarethecircle]

Originally, I strongly agreed that Erin was a TS or STS over the state until recent research revealed new information. I recently consulted another board, and a meteorologist mentioned Erin actually featured a weak cold core over Oklahoma, which may have been a primary factor the TPC's "remnant low" classification (in addition to the data in the TCR) over the state. If a warm core was present, I would have maintained my original stance.

If this is correct, Erin was NOT a TS or STS over the state.

Ahem,

http://en.wikipedia.org/wiki/Subtropical_cyclone#Types

Twice mentioned are cold core lows.

[MiamiensisWx]

Well, the TPC is obligated to remain consistent with their definitions. The main problem arises when physics never conform to those stringent standards.

I must admit that it is inconsistent to classify Erin as a "remnant low" when Allison (which was also very briefly well organized) was posthumously classified as a subtropical storm over land in Mississippi.

[Wthrman13]

Originally, I strongly agreed that Erin was a TS or STS over the state until recent research revealed new information. I recently consulted another board, and a meteorologist mentioned Erin actually featured a weak cold core over Oklahoma, which may have been a primary factor the TPC's "remnant low" classification (in addition to the data in the TCR) over the state. If a warm core was present, I would have maintained my original stance.

If this is correct, Erin was NOT a TS or STS over the state.

I'd be interested in seeing the evidence that Erin was a cold-core system. Everything I've looked at to date indicated that it indeed had a warm core, at least in the mid-levels. The 0Z 500 mb analysis for this day indicated a small warm core:

[MiamiensisWx]

The cold core was analyzed at the low levels (700-1000 mb). I believe that is most important for the classification of a TS/STS, if I recall correctly.

Can you post more charts and analyses of the 700-1000 mb levels for Erin over Oklahoma?

[Wthrman13]

The cold core was analyzed at the low levels (700-1000 mb). I believe that is most important for the classification of a TS/STS, if I recall correctly.

Can you post more charts and analyses of the 700-1000 mb levels for Erin over Oklahoma?

You can find some of these plots at the SPC page for this event:

http://w1.spc.woc.noaa.gov/exper/archiv ... index.html

The 850 and 700 mb plots show a west-east gradient in temperature, as is typical when moving west to east from the higher terrain in NM and TX to OK. This may have masked any signature associated with the cyclone itself, at least in this coarse resolution analysis. The 925 mb analysis does appear to show a weak cold core, but this is so near the surface that it is likely picking up near-surface conditions, possibly a weak cold pool. I would have to go back and review the surface data leading up to the event to determine for sure.

Note also that this analysis several hours before the storm was near its peak. It is likely that the rapid increase in convection near the core intensified the warm core at mid-levels, which is exactly what happens in a "legit" TC. For a system like this over land, typically the lack of a continuous surface latent and sensible heat flux and the fact that the low-levels are typically unsaturated, results in significant cold pool production, and thus a low-level cold core. In this case, however, area soundings indicate that the low-levels were nearly saturated, reducing the potential for evaporative cooling, although melting of hail may still have contributed to a cold pool. Surface observations indicate very weak cold pools, if any, associated with the convective bands and in and around the core of the storm as it intensified. This is likely what allowed the storm to intensify so rapidly and have such strong convergent surface inflow. Typical continental MCV's are impeded from developing down to the surface by the divergent cold pool outflow at low-levels, but this was not the case with Erin.

EDIT: I might also mention that OK had received a lot of rainfall in the days leading up to Erin, and many places had standing water. Evapotranspiration from the surface (latent heat flux) was very possibly a contributing factor to its intensification in much the same way as from a TC over warm water.

When I have time, I might try to put together some objective analyses in an effort to confirm (or disconfirm) the warm-core nature of the system. I am also active on a severe weather board, and the consensus there amongst the pro mets (most of which have much more experience than I) is that it was indeed warm core.