Subject: questions for presenters
Date: Mon, 05 Aug 2002 17:07:06 -0400
From: "Colin J Mcadie" <Colin.J.Mcadie@noaa.gov>
Organization: Tropical Prediction Center
To: "Edward.N.Rappaport" <Edward.N.Rappaport@noaa.gov>,
     "John.L.Beven" <John.L.Beven@noaa.gov>,
     "James.M.Gross" <James.M.Gross@noaa.gov>,
     "Richard.J.Pasch" <Richard.J.Pasch@noaa.gov>,
     "Brian.R.Jarvinen" <Brian.R.Jarvinen@noaa.gov>,
     "Colin.J.McAdie" <Colin.J.McAdie@noaa.gov>,
     Christopher Landsea <Chris.Landsea@noaa.gov>,
     James Franklin <James.Franklin@noaa.gov>,
     Mark Powell <Mark.Powell@noaa.gov>,
     Peter Black <Peter.Black@noaa.gov>

Presenters,
The best-track committee would greatly appreciate your response to
several follow-up questions arising from your presentations of last
Thursday.   Although these questions are posed to individuals, everyone
is invited to respond so at we may have the best possible basis for a
decision.  If you could respond by Wednesday it would be appreciated, as
the committee will meet again on Thursday.
1) To Mark:
The crux of our debate seems to center upon where the marine-land
transition occurs.   In your set of '96 W&F papers, we find the
following:
(part II, p. 332)
"According to the analysis in Fig. 3c, Andrew's maximum winds were in
the northern eyewall near Perrine where onshore flow
reached a maximum of 66 m/s on the coast and then decreased to 62 m/s
just inland.   The difference
between land and marine winds in the vicinity of the eyewall are
relatively small due to comparable roughness lengths
for marine and open terrain in high winds, as discussed in Part I."
(emphasis added)  Mark, if you were to write this paper today, would you
state this
differently?   It seems to contradict the discussion on Thursday.
In referring to Part I, there is another interesting discussion in 4.a.
Determination of Exposure in which there is a discussion of the
anemometer (LLWAS) cluster at MIA, with varying exposures, two of which
have suburban exposure, one open-terrain (close to the runway).  When the
wind is out of the north, roughless lengths performed
well in normalizing all three to a standard height.   "However, when the
wind veered to the northeast, open-terrain-adjusted winds at FA2 and
FA4......failed to compare with
FA1.   Apparently, the distant marine fetch
(even at 20-30 km upwind) became important, and roughness lengths had to
be reduced."   If marine effects are felt that far inland, does this argue
that marine effects would dominate on the immediate coast?
You also note:
"In a hurricane the flow trajectory is complicated by the additional
accelerations associated with the pressure field, the radial
distance from storm center, and convective components associated with
updrafts and downdrafts in the eyewall and
rainbands."    The above could also be taken to mean that there is very
little, or
possibly no, transition very near the coast in the core area.  Does this
agree with your current thinking?

2) To James:
Based on your preliminary analysis of dropsonde profiles in coastal
regions versus those in a purely marine environment, do you now have
some uncertainty in the use of a constant reduction factor for flight
level winds in near-coastal regions?

3) To Pete:
Why did you feel that you could quantitatively convert (or interpret) a
surface wind over land from marine
observations, but Mark could or would not?  That is, your document says
"multiplying this by the mean over land to over water ratio of 0.92
+/-0.8..."

3) To all: How should the apparent strengthening seen in the surface
pressure and satellite data after the 0810 UTC 162 kt
flight-level wind be interpreted in terms of the wind field?  Also, what
effect, if any, should the strong cells forming along the coast in the
northern eyewall have had on the surface wind field at the shoreline?

We realize your time is valuable.  Thank you for helping in this process.

Colin




  Colin McAdie 
  Research Meteorologist
  NOAA/NWS/Tropical Prediction Center