# Presentation: 670981

## The Case for Cat 5

- Brief review of the basis for the 90% solution.
- Application to Andrew for interpretation of flight-level data.
- Other measures: radar tracking, storm surge.
- Dvorak estimates, pressure-wind relationships.

## Franklin et al, 2002, W&F, submitted.

**Franklin et al, 2002, *****W&F*****, submitted.**
**429 eyewall sondes from 1997-99.**

## 429 eyewall soundings

- Release point tends to be slightly inward of the FL RMW.

## Majority of sondes released on the right-hand (stronger) side.

## Radial location in the eyewall strongly influence the mean profile shape.

## The 90% Rule

- R700 in eyewall = 91.5%, but is probably high due to sampling bias.  R700 at the FLRMW = 88%, represents lower bound if no azimuthal dependence: (88.0-91.5%)
- Right quad R700 lower than left by 0.037.  If this difference is valid at the RWM, then range valid for the right side would be (86.5%-90%).
- Midpoint of this range is ~88%.  Since maximum 700 mb wind probably wasn’t observed, recommended adjustment rounds up to 90%.

## Fraction of the peak BL wind that gets to the surface is a function of wind speed.

- Above about 110 kt, ratio of surface to BLTOP wind speed goes up.

## Adjustment factors also go up with increasing eyewall vertical motions.

**Adjustment factors also go up with increasing eyewall vertical motions.**

## Current best track is in very poor agreement with the adjusted recon winds.

**Current best track is in very poor agreement with the adjusted recon winds.**

## 3 min of 10-s obs supporting C5 (0809-0811Z); 1-m mean FL wind reduces to 143 kt. 

**3 min of 10-s obs supporting C5 (0809-0811Z); 1-m mean FL wind reduces to 143 kt. **

## 0810Z

**Pressure continued to fall after last recon of 932 mb at 0810Z.  Min pressures over land were 922 mb.  There is no reason to think that the flight-level winds decreased after the last fix.**

**Dvorak MSLP estimates way off (~15 mb or ~15 kt).**

## Assume that peak radar velocities occurred at the BL top, reducing using mean eyewall profile gives 134 kt.  Using a reduction more appropriate for the BL wind speeds gives 146 kt

**Assume that peak radar velocities occurred at the BL top, reducing using mean eyewall profile gives 134 kt.  Using a reduction more appropriate for the BL wind speeds gives 146 kt**

- Courtesy Peter Dodge

## Two proposed new peak winds fall within the historical scatter of Dvorak classifications.

- Dvorak-based pressure estimates were systematically to weak for Andrew.

## Proposed new pressure-wind pairs fall within the observed historical scatter, and are on the high-wind side of the mean curve, which is to be expected given Andrew’s size and environmental pressure.

## Concluding remarks

- If a current storm presented the same observations, there is little doubt that it would be evaluated as a Cat 5 hurricane, with maximum winds of 145 kt (+/- 5 kt).  There are insufficient contradictory surface obs to suggest that a 90% eyewall adjustment is inappropriate.
- No storm’s intensity can be determined with precision, and indirect measures must almost always be used.  A lack of certainty should not be an obstacle to revision of earlier estimates that are no longer consistent with current understanding.