The large number of radial flight legs over two days at the same flight level (850 hPa) made it possible to examine the changes in storm structure that occurred as Elena intensified from a disorganized category 2 to an intense category 3 hurricane. In the plots below, changes in Elena’s symmetric storm structure are examined by constructing radius-time Hovmollers of azimuthally averaged quantities collected during the reconnaissance missions.

Azimuthal averages were calculated by dividing the time period of study into four-hour bins and averaging all radial flight legs that occurred in each bin. The average number of flights that occurred in each four-hour window was seven, so that each quadrant of the storm was sampled at least once. The four hour azimuthal averages were smoothed with a 9 point Bartlett filter which removes features with wavelengths less than ~5 km. The averages are shown from the eye out to 150 km, and missing data always appears as dark blue in the Hovmollers below.

As a reminder, Elena was slowly intensifying between 00 and 18 UTC 31 August and rapidly intensifying until 00 UTC 2 September, after which the storm filled slowly until landfall (~13 UTC 2 September) according to the best track data set.

The height of the 850-hPa surface remains steady through 01 UTC 1 September when rapid height falls begin in the inner 25 km. Outside the inner core, the height gradient increases throughout the time period. The plot shows that Elena reached its maximum intensity, in terms of minimum 850 hPa height, ~20 UTC 1 September.

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The maximum tangential wind speed moves radially inward from 70 to 25 km. The wind speed increases rapidly starting 07 UTC 1 September as does the gradient of tangential wind within 25 km of the eye. Peak intensity at 850 hPa is between 03 and 07 2 September, well after the best track peak intensity at 18 UTC 1 September.

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Little change in the radial distribution of relative vorticity occurs until Elena starts to rapidly intensify around 01 UTC 1 September. After this time, the vorticity grows within the eyewall in a narrow (5-7 km) ring around the eye to greater values than

60 x 10^-4 s^-1.

Throughout Elena’s intensification, the inner 150 km is dominated by outflow at 850 hPa. Weak inflow is seen intermittently, and only from 13 - 19 UTC 1 September reaching the inner core. Given the upward motion seen in the figure below, strong inflow must have been confined below the

850-hPa level.

Much of the inner 150 km of Elena is covered with upward motion throughout the storms intensification. A strong eyewall updraft channel is seen beginning ~07 UTC 1 September. The very strong downdraft centered on 100 km between 01 and 07 UTC 1 September is a real feature, whose existence remains unexplained as of yet.

The warmest temperatures at 850 hPa within the eye of Elena occur between 07 and 13 UTC 1 September, 12 hours before peak intensity. This is possibly due to the raising of the height of the inversion in the eye with intensification of the storm.

Very little change occurs to the dew point in Elena with time, except within 50 km of the center where the values and gradient increase, especially after 01 UTC 1 September. The region of maximum dew points begins in the eyewall and moves radially inward with time, eventually spanning the entire region from the eye to the eyewall.

A minimum in relative humidity exists within the eye of Elena for 24 hours between 13 UTC 31 August and 13 UTC 1 September, after which the relative humidity sharply increases within the eye due to lower temperatures and higher dew points possibly due to eye/eyewall mixing. Outside the eye, relative humidities exceed 98% over much of the inner 150 km.

Most of the changes in the distribution of theta e in Elena occur within the inner 50 km. Maxima in theta e occur in the eyewall and eye of Elena between 07 and 13 UTC 1 September, and again in the eye from 19 UTC 1 September through 07 UTC 2 September. The radial gradient of theta e is maximized in the eyewall and moves radially inward with time.