Tuesday, September 20, 2005

	Rita was upgraded to a hurricane this morning.  It has gotten better-organized on 
satellite imagery (Fig. 172), with deep convection surrounding the core and the 
suggestion of an eye forming.  The eye shows up clearly on coastal radar (Fig. 173).  Rita 
is moving through the Florida Straits, crossing the Florida Keys as a Category 1 
hurricane.  The deep-layer steering flow (Fig. 174) indicates that Rita will continue this 
general westward motion and emerge into the southeastern Gulf of Mexico.  
Environmental conditions remain favorable, with light-to-moderate shear (Fig. 175) 
combining with high SSTŐs and low-level moisture to provide a favorable environment 
for continued intensification.

 

Figure 172.  GOES-East infrared image valid 1245 UTC September 20.

Today there was a NHC-tasked SFMR mission into Hurricane Rita.  N43RF 
performed this mission.  The NRL P-3 did not fly today, since the proximity of the storm 
to Florida and Cuba would limit room for maneuvering.  N42RF was still down this day, 
continuing the replacement of one of its engines.  The plan for N43RF was to fly a single 
figure-4 pattern, beginning on the northwest side, with 105 nm leg lengths.  An HRD 
sonde would be dropped at Key West and in each eyewall quadrant.  NHC has requested 
a drop in the northwest eyewall.  The aircraft would also do an overflight of Key West, 
for comparison of the tail radar Doppler velocities with Key West velocity/azimuth 
displays (VADs).  The aircraft would fly at 8000 ft.
 

Figure 173.  WSR-88D radar for Key West valid 1300 UTC September 20..

 

Figure 174.  CIMSS-derived 250-850 hPa layer-averaged wind (shaded, kt) valid 09 UTC 
September 20.
 

Figure 175.  CIMSS-derived 850-200 hPa vertical shear (shaded, kt) valid 09 UTC 
September 20.

	The pattern was flown as planned, with a modification to account for the 
proximity of the storm to Cuba (Fig. 176).  During the flight the storm was getting better 
organized.  The surface wind maximum was 90 kt on the southeast side of the storm.  
There was a marked asymmetry in SFMR-derived winds between the northwest and the 
southeast side, as peak SFMR-derived winds on the northwest side were 65 kt and peak 
SFMR-derived winds on the southeast side were 90 kt.  The eyewall was open on the 

 

Figure 176.  Plot of flight track for N43RF on September 20.
north side, as indicated by both lower fuselage and Key West 88D radar (Fig. 177).  The 
slope of the eyewall on the southeast side was nearly vertical, while on the northwest side 
it was more horizontally-sloped.  The combination of the surface wind asymmetry, lower 
fuselage radar pattern, and differences in the slopes of the southeast and northwest 
eyewall all suggest the possibility that the storm is experiencing some easterly or 
southeasterly shear.  Also evident on the Key West radar is a principal rainband spiraling 
in from the southeast, around to the north side of the storm.  The rain in the band is 
predominantly stratiform on the north side of the storm but is mostly convective on the 
upwind side of the band (i.e., east side of the storm).  Multiple bands were also evident 
on the southwest side of the storm.

 

Figure 177.  WSR-88D radar for Key West valid 2114 UTC September 20

	The initial pass through the storm showed a double eyewall structure, with the 
outer eyewall open on the north side and the inner eyewall open on the east and southeast 
side.  On subsequent passes the outer eye became more elliptical, rotating cyclonically as 
the flight progressed.  The MSLP dropped to 976 hPa, and the peak surface winds (as 
observed by the SFMR) was 90 kt on the southeast side of the storm.
	A total of 6 HRD sondes was dropped, included one in each eyewall pass and one 
at Key West.  This was a successful mission, as it accomplished the objectives of the 
tasking and sampled a storm that was complex and highly-evolving.  The presence of the 
principal rainband on the northeast side and the multiple bands in the south are both 
possible targets for a joint IFEX/RAINEX research mission planned for the following 
day.