Six-Hourly PV Overview of the Development of Flagler Beach Storm
Numerous studies have shown that rapid cyclogenesis results from the
interaction between baroclinic forcing and diabatic processes (latent heat
release and sensible heat flux). Latent heat release appears to be one of
the most significant factors in rapid cyclogenesis, especially oceanic
cyclogenesis. (Uccellini 1986; Reed et al. 1988; Kwo et al. 1991).
Since low level baroclinicity and moisture (for latent heat release), are
important factors in rapid cyclogenesis, the diagnosis of the evolution
of baroclinic zones and moisture regions is important. One way to identify
low-level baroclinic zones and moisture is through the display of low-level
equivalent potential temperature (theta-e).
Since tropopause undulations can be traced by their relatively high values
of potential vorticity (referred to as a PV anomaly), the overlay of potential
vorticity on the display of low-level theta-e can be used to identify
regions were interaction between tropopause undulations and low level
baroclinicity and moisture is possible.
The following are six-hour-forecast maps from the 00Z December 14, 1997
ETA model run.
320-324K isentropic potential vorticity is shown as shades of blue
and red. PV values greater than 1.0 suggest air of stratospheric origin.
Theta-e (in K) on the 300K isentropic surface is shown in green. Sea level
pressure contours (in mb) are shown in yellow. The wind barbs are wind
speed in knots on the 324K isentropic surface.
00Z December 14, 1997
Late on December 13, 1997, an area of high 320-324K isentropic potential
vorticity (a PV anomaly) was moving southeast into east Texas, Louisiana
and Mississippi. A baroclinic zone (identified by the sharp gradient in
theta-e), was located far to the southeast over the southeast Gulf of Mexico
and Florida. Weak surface lows existed along the baroclinic zone.
06Z December 14, 1997
12Z December 14, 1997
By 06Z on December 14, 1997, a weak surface low began to deepen off the
southwest Florida coast. The low tracked northeast to off the northeast
Florida coast by 12Z on December 14th. It will be shown later in this case
study that there is a possible relationship between the initial development
of the low and the PV anomaly due to slantwise vertical motion.
18Z December 14, 1997
00Z December 15, 1997
06Z December 15, 1997
12Z December 15, 1997
As the PV anomaly drew closer to the area of low level baroclinicity and
moisture, surface pressures off the northeast Florida coast began to fall
rapidly after 12Z on December 14, 1997. Between 12Z on December 14th and
18Z on December 15th, surface pressure fell from 1007 mb to 998 mb. The
Flagler Beach Pier was destroyed by high winds and waves around 12z on
the morning of December 15, 1997.
18Z December 15, 1997
00Z December 16, 1997
As PV anomaly moved over the top of the surface low, rapid deepening came
to an end after 18Z on December 15th. The minimum surface pressure was
996 mb.
To view an animated loop of all these maps, click
here.
The initial hypothesis was that tropopause undulations, especially their
associated temperature changes, can act synergistically with lower
tropospheric processes to initiate, maintain, and enhance the development
of extratropical cyclones.
Did the propagation of the PV anomaly, shown above, result in a
significant change in temperature in the upper troposphere?
