Hurricane and Severe Storm Sentinel (HS3) Field Campaign

The Hurricane and Severe Storm Sentinel (HS3) field campaign was a NASA mission that occurred over 5 northern hemisphere late summers, with the primary focus on 2012, 2013, and 2014. The HS3 campaign set out to investigate the processes underlying the formation and intensity change of Atlantic Ocean hurricanes. The focus was on the use of airborne instruments to measure storm-scale processes and large-scale environmental conditions. A variety of instruments were installed on two NASA Global Hawk high-altitude unmanned aircraft flown during selected hurricanes meeting the needed criteria of storm intensity and proximity to base.  HS3 included flights through Hurricanes Leslie and Nadine in 2012, Gabrielle, Ingrid, and Humberto in 2013, and Cristobal, Dolly, and Edouard in 2014. In addition, the WB-57 manned aircraft made serveral passes through Hurricane Gonzalo as a Cat 3 and Cat 4 storm during October 15-27, 2014.  

Scientific Objectives

The primary objectives of HS3 included:

  • Assessing the relative roles of large-scale environment and storm-scale internal processes
  • Addressing the role of the Saharan Air Layer (SAL) in tropical storm formation and intensification
  • Assessing the roll of deep convection in the inner-core region of storms
Spatial Coverage
[N: 52.0, W: -120.0, E: -60.0, S: 12.0] degrees
Time Range
September 6, 2012 - October 17, 2014

Instruments Used

Multiple instruments were flown on the Global Hawk UAV aircraft during the HS3 Field Campaign.  The instruments were used to observe either the tropical cyclone environment or inner-storm characteristics providing insight into storm development.  The instruments included a High Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP), a Hurricane Imaging Radiometer (HIRAD), a Cloud Physics LiDAR (CPL), a High-Altitude MMIC Sounding Radiometer (HAMSR), and a Scanning High-Resolution Interferometer Sounder (S-HIS).  In addition, Advanced Vertical Atmospheric Profiling System (AVAPS) dropsondes were released from the Global Hawk aircraft.  Support data were also collected during the HS3 campaign, consisting of various satellite, model output and operational datasets.



Global Hawk UAV







Tropical cyclone development

Tropical cyclone environment

Atmospheric temperature

Atmospheric humidity

Atmospheric Winds


Events of Interest

This section highlights events within the field campaign of particular scientific interest.

Major Findings

In September 2014, the Global Hawk flights of Hurricane Edouard captured a period of significant intensification. Data collected by both the instruments onboard the Global Hawk UAV and the AVAPS dropsondes released from the aircraft suggest that Edouard then weakened during the eyewall replacement cycle. The intensification and subsequent weakening were also seen in GOES imagery. The rapid variations in intensity occurred on much shorter time scales than those of the best-track data record.

Hurricane Nadine (September 2012) was the best chance for HS3 to study interactions between the Saharan Air Layer (SAL) and tropical cyclones. HS3 captured interaction of Nadine with the SAL that corresponded with two dust outbreaks exiting the Sahara. The CPL and the Scanning High-Resolution Interferometer Sounder (S-HIS) instruments detected a deep SAL within Hurricane Nadine’s northeastern quadrant revealed by its very hot and dry conditions lower in the layer and cooler, moister conditions near the top of the dust layer. It was not possible, however, to determine the impact of the SAL on Hurricane Nadine. 

The outflow of a tropical cyclone can play a role in a hurricane’s Maximum Potential Intensity (MPI). It is assumed that outflow stratification is the result of internal dynamics and small-scale turbulence which limits the Richardson number (Ri). The Ri expresses the ratio of buoyancy and wind shear. During HS3, the global hawk provided high-density coverage of the outflow layer, including a lower-stratospheric layer of low Ri, characterized by strong shear and higher stability not previously measured with typical dropsondes.

HS3 also obtained data useful for the study of the structure of the Saharan Air Layer and the environmental processes involved in determination of which systems fail to develop into hurricanes.

Related Publication(s)

Field Campaign Publication:
Braun, S.A., P.A. Newman, et al. (2016). NASA’s Hurricane and Severe Storm Sentinel (HS3) Investigation. BAMS, November 2016, 2085-2102. doi:

HS3 Notable Publications:
Abarca, S.F., M.T. Montgomery, et al. (2016). On the Secondary Eyewall Formation of Hurricane Edouard (2014). Monthly Weather Review, 144, 3321-3331. doi: 
Komaromi, W.A. and J.D. Doyle (2017). Tropical Cyclone Outflow and Warm Core Structure as Revealed by HS3 Dropsonde Data. Monthly Weather Review, 145, 1339-1358. doi:
Maskey, M., M. McEniry, et al. (2014). Data System for HS3 Airborne Field Campaign. 
Munsell, E.B., J.A. Sippel, et al. (2015). Dynamics and Predictability of Hurricane Nadine (2012) Evaluated through Convection-Permitting Ensemble Analysis and Forecasts. Monthly Weather Review, 143, 4514-4532. doi: 
Munsell, E.B., F. Zhang, et al. (2017). Dynamics and Predictability of the Intensification of Hurricane Edouard (2014). Journal of the Atmospheric Sciences, 74, 573-595. doi:
Raymond, D.J. (2016). The effects of moist entropy and moisture budgets on tropical cyclone development. Journal of Geophysical Research, 121:16, 9458-9473. doi:
Rogers, R.F., J.A. Zhang, et al. (2016). Observations of the Structure and Evolution of Hurricane Edouard (2014) during Intensity Change. Part II: Kinematic Structure and the Distribution of Deep Convection. Monthly Weather Review, 144, 3355-3376. doi: 
Zawislak, J., Haiyan J., et al. (2016). Observations of the Structure and Evolution of Hurricane Edouard (2014) during Intensity Change. Part I: Relationship between the Thermodynamic Structure and Precipitation. Monthly Weather Review, 144, 3333-3354. doi:
Background Hurricane Information:
Bender, M.A. (1997). The Effect of Relative Flow on the Asymmetric Structure in the Interior of Hurricanes. Journal of the Atmospheric Sciences, 54, 703-724. doi:;2 
Braun, S.A. (2010). Reevaluating the Role of the Saharan Air Layer in Atlantic Tropical Cyclogenesis and Evolution. Monthly Weather Review, 138, 2007-2037. doi: 
Didlake, Jr., A.C., G.M. Heymsfield, et al. (2015). The Coplane Analysis Technique for Three-Dimensional Wind Retrieval Using the HIWRAP Airborne Doppler Radar. Journal of Applied Meteorology and Climatology, 54, 605-623. doi:
Kaplan, J. and M. DeMaria (2003). Large-Scale Characteristics of Rapidly Intensifying Tropical Cyclones in the North Atlantic Basin. Weather and Forecasting, 18, 1093-1108. doi:;2
Kelley, O.A., J. Stout, et al. (2005). Tall precipitation cells in tropical cyclone eyewalls are associated with tropical cyclone intensification. Geophysical Research Letters, 31(24), L24112. doi: 
Molinari, J. and D. Vollaro (2010). Rapid Intensification of a Sheared Tropical Storm. Monthly Weather Review, 138, 3869-3885. doi:


Nov 15th, 2018
Leigh Sinclair
Field Campaign

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