Shown below is a time series of the percent of area covered by >30 and >40 dBZ within 75 km of the center of Elena, constructed in order to investigate changes in the areal coverage of convection within the storms core.

The red line and left scale is the percentage of area covered by >30 dBZ, while the blue line and scale to the right represent the area covered by >40 dBZ. Breaks in the time series represent times without radar data. The percent of area covered by >30 dBZ steadily increases with time to a peak value of 55% by 11 UTC 1 September. During the same time period, the area covered by >40 dBZ shows several spikes, but shows no upward trend and averages ~.75%. After 13 UTC, the area covered by >30 dBZ decreases slightly and remains steady around 40% through 02 UTC 2 September. However, the area covered by >40 dBZ undergoes a dramatic increase in the same 12-hour period. A sharp increase begins ~16 UTC and the peak in coverage (~6%) occurs at 18 UTC, after which the coverage of deep convection decreases steadily until the end of the period of study. This increase and then peak in the coverage of deep convection within Elena’s core is coincident with the rapid intensification and maximum tangential wind speeds (from 850 hPa flight level recon data) found in Elena, shown below.

Analysis of the radar images from Apalachicola, FL shows that the increase in deep convection was not symmetric about Elena’s center. Rather, it was concentrated in the northern eyewall, as the long-term time averaged radar reflectivity plot shows below (averaged 1310-2355 UTC 1 September).

To quantify the changes in deep convection in various quadrants of Elena, time series of the percent of area covered by >40 dBZ within 75 km of the center were constructed with respect to both true geography and the direction of vertical wind shear. In the graph below, the “NW” (“NE”) quadrant represents the 90° wedge directly to the left (right) of due north.

Concentrating now on only the time period after 13 UTC, it is clear to see that the increase in area covered by >40 dBZ is primarily coming from the northern half of Elena’s circulation. The NW quadrant shows the largest increase (15%) and remains high even after the percentage in the NE quadrants starts to drop off. The SW quadrant shows a modest increase in coverage after 19 UTC while deep convection in the SE quadrant is almost non-existent through the time period.

With respect to vertical wind shear, the quadrants are oriented such that the division between quadrants lies along the shear vector, or that “downshear left” represents the 90° wedge counterclockwise from directly downshear to left of the shear vector. As can be seen below, the direction of vertical wind shear in Elena was from the northwest throughout the period of study.

Again looking at only the time period after 13 UTC, the increase in the coverage of deep convection is initially confined to the upshear left quadrant, with a later increase in coverage in the upshear right quadrant as the convection seems to rotate cyclonically around the storm with time. Small peaks in the coverage are seen in the other two quadrants, but overall the areal coverage of deep convection in the downshear quadrants remains low.