Wednesday, September 21, 2005

On Wednesday morning, Hurricane Rita appeared much stronger from satellite 
imagery.  Infrared imagery (Fig. 178) showed that Rita had a large (30-40 nm diameter) 
eye with very cold cloud tops.  Such a satellite signature is indicative of a major 
hurricane.  Microwave data collected several hours earlier (Fig. 179) showed that there 
was a principal rainband spiraling around the storm and extending out hundreds of miles.  
The heaviest rainfall associated with the rainband was located on the north side of the 
storm.  A radar image from Key West that morning (Fig. 180) also showed the band on 
the east side of the storm, along with several other banded features in the east and 
northeast sections of the storm.  Shear is still weak over the storm (Fig. 181), and track 
guidance (Fig. 182) predicts that Rita will continue into the Gulf, where waters are still 
very warm.  Thus Rita is expected to remain a significant hurricane in the Gulf, possibly 
making landfall in the northwestern Gulf in about three 3 days.

 

Figure 178.  GOES-East infrared image valid 0845 UTC September 21.

	The plan for today called for a two-plane IFEX/RAINEX mission into Hurricane 
Rita.  N43RF would fly a figure-4 pattern, with an IP 50 nm east of the storm.  That 
pattern would end up on the north side of the storm, after which point N43RF would 
begin to work with the NRL P-3 on rainbands around the storm.  The two aircraft would 
fly rainbands in all quadrants, if possible, and then N43RF would finish with another 
figure-4 with the same orientation as the first one.  N43RF would fly at 12,000 ft, and the 
NRL P-3 would fly at 14,000 ft.  If icing became a problem, then NRL would descend to 
12,000 ft, and N43RF would descend to 8000 ft.  RAINEX drops would be made in the 
middle of the eyewall and on the inner edge of the eyewall, at the center of the storm, and 
at the midpoint and endpoints of any rainband legs that are flown.  HRD drops would be 
made at all turn points in the figure-4 patterns.  Nine AXBT's are available; they will be 
dropped just outside the eyewall on the first figure-4 and at the midpoint of each rainband 
leg.
 

Figure 179.  SSM/I 85 GHz image valid 0154 UTC September 21.

 

Figure 180.WSR-88D reflectivity (shaded, dBZ) from Key West valid 0927 UTC 
September 21.
 

Figure 181.  CIMSS-derived 850-200 hPa vertical shear (shaded, kt) valid 06 UTC 
September 21.
 
Figure 182.  Track guidance for Hurricane Rita valid 06 UTC September 21.



	The mission did follow the plan well.  The flight tracks shown in Figure 183 
indicate that N43RF did fly its two figure-4 patterns as well as fly along rainbands in all 
four quadrants.  The NRL P-3 flew primarily around the periphery of the core, which was 
according to plan as well.  The storm was undergoing rapid intensification prior to and 
during the flight today.  The final fix in the previous day's mission had a central pressure 
of 972 hPa, while the first pass in today's mission (less than 24 h later) had an 
extrapolated MSLP of 925 hPa Ð nearly 50 hPa in less than 24 h.  During the first 
penetration there was an indication that there was a double eyewall present, but there was 
no secondary wind maximum at the time.  Rainfall was primarily stratiform in the 
northeast side.  As usual, marked azimuthal asymmetries in the wind field were evident, 
as peak flight-level winds on the east (west) side were 140 (120) kt, while peak SFMR 
winds were 125 (110) kt.    Peak flight-level winds on the north (south) side were 160 kt, 
while peak SFMR winds were 130 (120) kt.  The eye for the entire mission had a good 
stadium effect.  By the time of the second figure-4 near the end of the mission, the peak 
flight-level winds on the east (west) side were 160 (150) kt, while peak SFMR winds 
were 135 (130) kt Ð a 20-30-kt increase in flight-level winds and 10-20-kt increase in 
surface winds in a 3-h time period.  The MSLP had also dropped from 928 hPa to 909 
hPa, as measured from GPS sondes, over this same time period.  Sea-surface 
temperatures measured from the AXBT's generally were 28.5 -29 C ahead of the storm, 
indicating an ocean environment favorable for sustaining a storm of this strength.


 

Figure 183.  Tracks of N43RF and NRL P-3 for flight on September 21.
	The coordination between the two aircraft for the rainband work was a bit clumsy 
at first, largely because there was such widespread stratiform rain in the north side of the 
storm.  Coordination was eventually established, however, and some excellent patterns 
were flown around the rainbands on the northwest, southwest, and southeast sides (Fig. 
184).  The passes in the northwest quadrant included both downwind and upwind legs.  
Portions of these passes were well-enough coordinated to provide quad-Doppler 
coverage.  A total of 35 sondes and 9 AXBT's were dropped in the storm as it completed 
its cycle of rapid intensification.  Shortly after the mission was completed, the minimum 
central pressure observed by an Air Force aircraft was 897 hPa, marking the fourth-
lowest central pressure ever recorded in the Atlantic basin.  This mission should provide 
an excellent dataset for studying the evolution that occurs with rapid intensification.  It is 
also the third mission in three days into this system, which was first sampled as a tropical 
storm and has now become a Category-5 hurricane in less than three days.

 
Figure 184. Plot of lower fuselage reflectivity (shaded, dBZ) from N43RF and flight 
tracks of N43RF and the NRL P-3 during previous 30 minutes for (a) 1650 UTC; (b) 
1720 UTC; (c) 1735 UTC; and (d) 1900 UTC September 21, 2005.


Thursday, September 22, 2005

	Hurricane Rita continues as a Category 5 today.  Infrared satellite imagery (Fig. 
185) shows a symmetric, intense storm.  Outflow may be somewhat restricted on the 
south side.  A TRMM overpass from the morning (Fig. 186) shows a concentric eyewall 
structure and two well-defined bands extending around the north and to the east side of 
the storm.  There is some southerly vertical shear impacting the storm (Fig. 187), but it is 
light.  The forecast call for Rita to maintain its intensity or weaken some before making 
landfall along the northern Texas coast sometime early Saturday morning.

 

Figure 185.  GOES-East infrared image valid 0815 UTC September 22.

	The engine on N42RF has been replaced and tested, and the aircraft is ready to 
fly.  Consequently, a three-plane mission is planned.  N43RF will fly a mission with 
multiple objectives.  The primary objective is to conduct an NHC-tasked fix/SFMR 
mission with fix responsibilities at 15, 18, and 21 UTC.  Piggy-backed onto this tasked 
mission is a module to map out the sea surface temperature and subsurface temperature 
structure with 18 AXBT's dropped at locations meant to coincide with where the Air 
Force dropped drifting buoys the previous day.  Eight of those AXBT's will be deployed 
in combination with HRD dropsondes.  RAINEX objectives will also be met by 
providing lower-fuselage radar coverage and by dropping RAINEX sondes at the flight-
level wind maximum in the eyewall, and, if there is a secondary eyewall, in the secondary 
wind maximum and in the moat region between the two eyewalls.  NHC sondes will also 
be dropped at the surface wind maximum in the eyewall and at the center of the storm.
 

Figure 186.  TRMM 85 GHz microwave brightness temperature (shaded, K) valid 1442 
UTC September 22.


 

Figure 187.  CIMSS-derived 850-200 hPa vertical shear (shaded, kt) valid 03 UTC 
September 22.
	The mission for N43RF proceeded as intended.  Because the storm was moving a 
little more slowly than anticipated, the pattern was extended by about 50 nm on the 
northwest side (Fig. 188) to allow for dropsonde and BT drops coincident with the 
placement of the Air Force buoys.  The figure-4 was repeated after that northwest leg, 
beginning on the southwest side instead of the northeast side.  After finishing that figure-
4 and ending up on the southeast side, N43RF came north on a downwind leg to a point 
northeast of the storm.  It then flew its last pass inbound, then outbound to the east, and 
finally returning to base.  There were a total of 8 HRD sonde/AXBT combination drops, 
plus ten more AXBT's were dropped.  During the flight some slight weakening from the 
previous day was noted, though MSLP continued to hover between 910 and 915 hPa 
from GPS sonde drops.  The eye did remain clear however, with a good stadium effect 
evident.  Low-level clouds were more prevalent in the eye, though, and the inner eyewall 
was open on the southeast side.  Peak flight-level winds were 135 kt in the northeast 
eyewall, while peak surface winds (measured by the SFMR) were 120 kt in the northwest 
eyewall.  The storm developed a classic concentric eyewall pattern.  With each 
successive pass the development of an outer wind maximum was sampled.  An 
interesting pattern was noticed, however, in that the outer wind maximum was clearer on 
the south side than on the north side.  By the end of the flight, the reflectivity gradients 


 

Figure 188.  Plot of flight tracks for N43RF, N42RF, and NRL P-3 on September 22, 
2005.

had sharpened up significantly and the flight-level winds in the inner and the outer 
eyewall were of comparable magnitude, both on the south and the north side of the storm.  
There was a marked asymmetry in the SFMR winds noted in the inner eyewall, with 
surface winds of 120 kt on the northwest side and only 85 kt on the southeast side.  Sea-
surface temperatures ahead of the storm were 29-29.5 C with a deep mixed layer.  These 
dropsonde and BT measurements, in conjunction with the buoys deployed by the Air 
Force, should provide valuable data of the oceanic conditions underneath and in advance 
of a major hurricane in the Gulf
In addition to N43RF, N42RF and the NRL P-3 were also in the storm, providing 
detailed coverage of the inner core as well as the outer rainband regions (cf. Fig. 188).  
N42RF was flying an Ocean Winds experiment, so it spend much of its time sampling the 
eyewall (both inner and outer) in radial legs.  There were some instances where it flew 
downwind legs over a small azimuthal range.  The lower fuselage radars from both 
N42RF and N43RF were used to guide the NRL P-3 in its RAINEX mission.  The NRL 
P-3 flew a pattern that should yield rich datasets for future research.  It flew in the moat 
region in between the inner and outer eyewall (Fig. 189), completing several 
circumnavigations of the inner eyewall.  While this was occurring, N42RF was sampling 
the eyewall and moat region at high temporal resolution, while N43RF was providing the 
broader context of the hurricane with its tasked figure-4 patterns.  The proximity of the 
NRL P-3 to the inner eyewall during its circumnavigations was generally less than 10-15 
km, which would provide excellent tail Doppler coverage of this feature.  During these 
patterns, N43RF was dropping sondes within the inner eyewall, along the inner edge of 
the outer eyewall, and within the moat region between the inner and outer eyewall, the 
NRL P-3 was dropping sondes all along the moat region during its circumnavigation, and 
N42RF was dropping sondes within the eyewall and along the inner and outer eyewall 
when it was making downwind legs.  From these patterns it is clear that excellent 
coverage of all four quadrants of this hurricane was achieved by the three aircraft.

 


Figure 189.  Plot of lower fuselage reflectivity (shaded, dBZ) from N43RF and N42RF 
and flight tracks of N43RF, N42RF, and the NRL P-3 during previous 30 minutes for (a) 
1645 UTC; (b) 1730 UTC; (c) 1930 UTC; and (d) 2000 UTC September 22, 2005.

Friday, September 23, 2005

	Hurricane Rita continues to approach landfall in the northwestern Gulf of Mexico 
as a major hurricane.  Satellite imagery (Fig. 190) continues to show a clear eye 
indicative of a strong storm, though it appears from this image that outflow on the south 
side is being restricted.  Such a restriction is indicative of southerly shear. This is 
supported by the CIMSS shear analysis (Fig. 191), which shows moderate (15-20 kt) 
southerly shear impacting the storm.  Satellite microwave imagery (Fig. 192) indicates 
that the outer eyewall seen on the previous day may be eroding and has expanded to 
around 100 nm in diameter.  The inner eyewall shows an asymmetry, with an opening on 
the southeast side.  An analysis of surface winds produced from the overnight hours (Fig. 
193) shows that maximum surface winds are around 110 kt on the northeast side of the 
storm.
	
 

Figure 190.  GOES-East infrared image valid 1015 UTC September 23.

	Today there was another tasked mission for N43RF.  N42RF would fly another 
Ocean Winds experiment, and the NRL P-3 would again fly, using the LF radars from 
both NOAA P-3's to guide it.  N43RF's mission is a combination SFMR/fix mission into 
Hurricane Rita, with fix responsibilities at 18, 21, and 00 UTC.  The leg length would be 
105 nm, with an IP on the northeast side.  GPS sondes would be dropped for NHC at the 
surface wind maximum on the northeast and northwest sides, plus drops in the center.  In 
addition to these operational responsibilities, several research objectives would be met as 
well.  RAINEX drops would be released at the flight-level wind maximum in the inner 
eyewall, in the moat region between the inner and outer eyewall (if an outer eyewall 
exists), and on the inner edge of the outer eyewall (if it exists).  Additionally, HRD 
GPS/AXBT combination drops would be released in the southwest and southeast 
quadrants during the first figure-4, corresponding to the drop locations from the previous 
day's drops and partially covering the buoy grid laid out by the Air Force two days 
earlier.  Finally, HRD sondes would be dropped on the downwind leg along the coast of 

 

Figure 191.  CIMSS-derived 850-200 hPa vertical shear (shaded, kt) valid 06 UTC 
September 23.

 

Figure 192.  AMSR-E AQUA 89 GHz microwave emissivity (shaded, K) valid 0808 
UTC September 23.

 
Figure 193.  H*Wind surface wind analysis valid 0730 UTC September 23.

Louisiana to provide the vertical profile of wind speeds upstream of wind profiling 
towers placed along the coast in anticipation of landfall.
	The N43RF mission followed the plan.  The IP was on the northeast side (Fig. 
194), and the aircraft dropped 11 HRD sonde/AXBT combination drops in the southwest 
and southeast quadrant of this initial figure-4.  At the completion of the figure-4 pattern 
the aircraft was on the northwest side.  At this point the aircraft turned downwind to the 
southwest side and headed inbound for the next figure-4.  It did a coastal run on the next 
downwind leg, dropping six HRD sondes along this downwind leg to support landfall 
objectives as outlined above.  The end of this figure-4 was on the southeast side, at which 
 

Figure 194.  Tracks of N42RF, N43RF, and NRL P-3 on September 23.

point the aircraft did a downwind leg to a point east-northeast of the center and came in 
for a final fix before returning to base.  All during the pattern N43RF dropped RAINEX 
sondes across the inner eyewall, in the moat region, and along the outer eyewall.  A total 
of 49 sondes (24 RAINEX, 10 NHC, and 15 HRD sondes) and 12 AXBT's were dropped.
	The storm had undergone significant structural changes from the previous two 
days.  The MSLP had risen to about 930 hPa.  Peak flight-level (surface) winds were 130 
(90) kt on the northeast side of the storm.  By contrast, peak flight-level (surface) winds 
were 100 (85) kt on the southwest side of the storm.  Concentric eyewalls still seemed to 
be present, but marked asymmetries developed as the storm encountered 15-20 kt of 
southerly shear (cf. Fig. 191).  This asymmetry was manifested in several ways: in the 
reflectivity pattern in the inner core, the rainfall distribution outside the core, the 
relationship between the radial location of flight-level and surface wind peaks in the 
different quadrants, and the difference between the flight-level and surface magnitudes in 
the different quadrants.  Toward the end of the flight, it appeared that the outer eyewall 
dissipated and was replaced by a band that was spiraling into the center on the west side 
of the storm.
	The other aircraft flew patterns similar to that flown yesterday (cf. Fig. 194).  
N42RF continued the Ocean Winds work of the previous day, primarily targeting the 
northern and southern inner eyewall.  The NRL P-3 again was able to circumnavigate the 
inner eyewall, flying in close proximity to the inner eyewall (Fig. 195).  In addition, the 
NRL P-3 was able to fly into the center of the hurricane, coming in through the opening 
on the south side of the inner eyewall.  All in all, these Rita flights have sampled a 
remarkable shift in the structure of the hurricane from a very strong, symmetric Category 
 

Figure 195.  Plot of lower fuselage reflectivity (shaded, dBZ) from N43RF and N42RF 
and flight tracks of N43RF, N42RF, and the NRL P-3 during previous 30 minutes for (a) 
1945 UTC; (b) 2100 UTC; (c) 2145 UTC; and (d) 2215 UTC September 23, 2005.

5 hurricane to a strong, symmetric, Category 4 hurricane with concentric eyewalls to a 
Category 2-3 hurricane that is developing asymmetries, possibly in response to vertical 
shear and/or dry air on the west side of the storm.   

Saturday, September 24, 2005

Today there were no flights.  Hurricane Rita made landfall at around 08 UTC 
Saturday.  There are no plans for flights during the next day.  N42RF is down for an 
inspection on Monday after encountering moderate turbulence in Friday's flight.  N43RF 
is planning a Gulf AXBT post-Rita survey mission on Monday, while the NRL P-3 is not 
anticipating flying in the next day or two.
Elsewhere in the Tropics it is relatively quiet.  There are no potential targets 
expected within at least the next day or two.  

Sunday, September 25, 2005

	In the Tropics there are three areas of activity but only one possible area for 
research flights.  An area of deep convection is located northeast of Bermuda that 
consists of the remnants of Philippe (Fig. 196), but this is likely become non-tropical and 
is not a factor for operations.  A tropical wave is located near 35 W, but that is not 
expected to develop into a tropical cyclone for several days, and it will likely be out of 
range for any operations.  The only system of possible interest for research operations is 
in the southeast Caribbean.  An infrared satellite image (Fig. 197) shows an area of deep 
convection located around 13 N 66 W.  This is in a climatologically unfavorable area for 
genesis, but the environment is characterized by low shear values (Fig. 198), so there is 
some potential for development.  A few of the NCEP ensemble members are predicting a 
tropical cyclone to form in the central or western Caribbean in the next 2-4 days (Fig. 
199).

 

Figure 196.  GOES-East water vapor image valid 1245 UTC September 25.

No flights are planned for today.  The only activity planned for Monday is a post-
Rita gulf survey pattern by N43RF, where 55 AXBT's would be dropped in the same area 
covered by the previous week's post-Katrina survey pattern and where the Air Force had 
laid out buoys several days earlier.
 

Figure 197.  GOES-East infrared image valid 1215 UTC September 25.

 

Figure 198.  CIMSS-derived 850-200 hPa vertical shear (shaded, kt) valid 09 UTC 
September 25.
 

Figure 199.  Plot of detection of vortices in GFS ensemble members for model runs 
initialized at 00 UTC 25 September 2005.

Monday, September 26, 2005

	Today N43RF flew the post-Rita Gulf survey pattern.  A total of 55 AXBT's were 
dropped, and 52 worked well.  This should provide valuable information about the 
response of the ocean to the passage of two major hurricanes in a three-week time period.
	The tropical wave in the Caribbean looks a little less organized today (Fig. 200).  
Infrared imagery shows a predominantly linear organization to the convection on the 
northwest side, with disorganized cold cloud tops trailing the line south of Hispaniola.  
QuikScat image (Fig. 201) does not show any significant circulation underneath the 
convection.  Vertical shear is still relatively low, however (Fig. 202), so it is still possible 
that this system could develop as it progresses toward the west and northwest.
	
 

Figure 200.  GOES-East infrared image valid 1315 UTC September 26.
 

Figure 201.  QuikScat surface winds (barbs, kt) valid 1346 UTC September 26.

 

Figure 202.  CIMSS-derived 850-200 hPa vertical shear (contours, kt) valid 09 UTC 
September 26.

Tuesday, September 27, 2005

	Today the system in the Caribbean looks bit better organized.  Visible imagery 
(Fig. 203) indicates a possible midlevel circulation south of the eastern tip of Cuba and 
east of the Honduras/Nicaragua border.  Infrared imagery (Fig. 204) shows an area of 
relatively concentrated deep convection mostly displaced to the east of this midlevel 
circulation.  QuikScat-derived winds (Fig. 205) show a cyclonic curvature to the surface 
winds, but no evidence of a closed circulation.  Vertical shear remains low over the 
system, however (Fig. 206) and the waters are warm, so the environment is favorable for 
continued development.  Track guidance for the system, should it develop (Fig. 207), 
brings it generally northwest toward the Yucatan peninsula within 3-4 days.  If the 
system does develop into a tropical depression, there would be interest to fly a RAINEX 
mission with the NRL P-3 and N43RF.  The mission would be along the lines of the 
Convective Burst module described in the 2005 HFP plan, similar to what was flown on 
the first day of the Ophelia flights.  Since there are limited flight hours left for the NRL 
P-3, however, only one mission would be possible.  The tasking of any such mission 
would occur only if a tropical depression forms, however.


 

Figure 203.  GOES-East visible image valid 1415 UTC September 27.

 

Figure 204.  GOES-East infrared image valid 1415 UTC September 27.


 

Figure 205.  QuikScat surface winds (barbs, kt) valid 1322 UTC September 27.

 

Figure 206.  CIMSS-derived 850-200 hPa vertical shear (contours, kt) valid 12 UTC 
September 27.

 

Figure 207.  Track forecast guidance for Caribbean system valid 12 UTC September 27.

Wednesday, September 28, 2005

	Whereas the Caribbean system looked promising yesterday, today it looks very 
disorganized.  Infrared imagery (Fig. 208) indicates that the system has returned to a 
more linear state.  The system has been following a pattern where concentrated 
convection develops during the daytime hours and then dissipates during the overnight 
hours.  This is opposite from the normal diurnal cycle of convective maximum during the 
overnight hours and convective minimum during the daytime hours.  One of the factors 
that may be playing an inhibiting role in the organization of convection is an upper-level 
cyclonic circulation located over Florida and extending into western Cuba (Fig. 209).  
This may be imparting some westerly shear on the northern part of the system that is 
preventing convection from developing and organizing.  If it does become a depression, 
however, track guidance (Fig. 210) generally brings it close to the Yucatan within 2 days.  
Because of the lack of organization of the system, no research flights are planned for 
tomorrow.  The last window of opportunity for flying is Friday.  If the system does 
become a tropical depression by tomorrow a mission may be tasked for Friday.  That will 
be dependent on how close the system is to land, however.

 

Figure 208.  GOES-East infrared image valid 1245 UTC September 28.
 

Figure 209.  CIMSS-derived cloud motion vectors for 100-500 hPa layer (barbs, kt) valid 
03 UTC September 28.

 
Figure 210.  Track guidance for Caribbean system valid 12 UTC September 28.

Thursday, September 29, 2005

	The system in the Caribbean has generally followed the same pattern as the 
previous couple of days.  Infrared imagery from the morning (Fig. 211) shows that 
convection remains disorganized.  This lack of organization has been somewhat puzzling, 
since the waters have been quite warm and the large-scale shear environment (Fig. 212) 
has been generally favorable, with shear values never getting above 15 kt.  Despite the 
seemingly favorable large-scale environment, however, a surface circulation still has not 
developed (Fig. 213).  As a result, the system is still not a depression, and thus no 
research flights are planned.  The difficulty in predicting the development of a tropical 
cyclone highlights our lack of understanding of tropical cyclogenesis and should serve as 
good motivation to continue research missions intended to improve our understanding 
and ability to predict tropical cyclogenesis events.
With no research missions planned, that marks the end of the HRD 2005 
Hurricane Field Program. 

 

Figure 211.  GOES-East infrared image valid 1245 UTC September 29.
 

Figure 212.  CIMSS-derived 850-200 hPa vertical shear (shaded, kt) valid 09 UTC 
September 29.

 

Figure 213. QuikScat surface winds (barbs, kt) valid 0812 UTC September 29.

 
 
 
 


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