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Wind Location and Radius Graphs
Maximum wind location by quadrant
Plot of storm maximum wind locations within the forecast area by quadrant of occurrence reveal that 8.5% (10 cases) occurred in the upper left quadrant, 10.2% (12 cases) occurred in the lower left quadrant, 29% (34 cases) occurred in the upper right quadrant and 52% (52 cases) occurred in the lower right quadrant. See below text for a detailed description
This graphic shows the frequency of maximum winds (in 117 cases) that occurred within the forecast area while the storm itself was also within the forecast area. There is a well-defined preference for the wind maxima to occur with greatest frequency in the eastern semicircle (81% of the cases). 52% of the cases had the maximum winds in the southeast quadrant. Conversely the northwest quadrant displayed the fewest cases with only 8.5%.
This pattern of winds fits well with what is characteristic of transitioning Tropical Cyclones the more northern latitudes: skewed, asymmetric wind fields typically displaying a larger and more intense wind field right of track. Increasing storm motion toward the north, northeast or east has an additive affect on wind speeds right of track and a subtractive affect on winds left of track. Additionally, wind radii expand and maximum winds spread out from the Tropical Cyclone core.
Threshold winds by quadrant
Bar graph of occurrences of threshold winds by quadrant and by count. The NE quadrant had 82 occurrences of gale force winds, 53 occurrences of storm force winds and 21 occurrences of hurricane force winds. The SE quadrant had 89 occurrences of gale force winds, 59 occurrences of storm force winds and 21 occurrences of hurricane force winds. The SW quadrant had 76 occurrences of gale force winds, 32 occurrences of storm force winds and 13 occurrences of hurricane force winds. The NW quadrant had 70 occurrences of gale force winds, 30 occurrences of storm force winds and 12 occurrences of hurricane force winds. See below text for a detailed description
This graphic illustrates the frequency of occurrence of threshold winds in each quadrant. The three important thresholds are: gale force (34-47 kt); storm force (48-63 kt); hurricane force (> 63 kt).
Additionally for gale force winds the NE and SE quadrants contain gale force winds about 15% more often than the SW or NW quadrants. The differences become greater for storm force winds with the NE and SE quadrants experiencing these winds up to 50% more often. For hurricane force winds this trend continues with the NE and SE quadrants experiencing hurricane force winds more than twice as often as the SW or NW quadrants.
These next three graphics show the radial distances in each quadrant for each of the three threshold winds. In all threshold cases for gale force, storm force and hurricane force wind radii the extent of these winds is greatest in the eastern semicircle.
Radial distance of gale force winds
Bar graph of average radial distance of gale force winds (34-47 kt) by quadrant for all storms reveals that there is an average distance of 230 nanometres in the NE quadrant, 266 nanometres in the SE quadrant, 204 nanometres in the SW quadrant and 132 nanometres in the NW quadrant
On average, gale force winds extend between 75% and 100% farther in the NE and SE quadrants than in the NW quadrant and 12% to 25% farther than the SW quadrant.
Radial distance of storm force winds
Bar graph of average radial distance of storm force winds (48-63 kt) by quadrant for all storms reveals that there is an average distance of 138 nanometres in the NE quadrant, 136 nanometres in the SE quadrant, 104 nanometres in the SW quadrant and 85 nanometres in the NW quadrant
Storm force winds in the NE and SE quadrants extend about 48% farther than in the NW quadrant and 24% farther than in the SW.
Radial distance of hurricane force winds
Bar graph of average radial distance of hurricane force winds (>64 kt) by quadrant for all storms reveals that there is an average distance of 116 nanometres in the NE quadrant, 71 nanometres in the SE quadrant, 59 nanometres in the SW quadrant and 61 nanometres in the NW quadrant
Hurricane force winds extend nearly twice as far in the NE quadrant than in the SW or NW quadrants. Hurricane winds tend to extend only 15% farther in the SE quadrant than the SW or NW.
An examination was also made of the differences in storm details between the entry point into the forecast area and the exit point … and snapshots of the wind fields were compared in order to determine how the wind fields evolved. The expectation was that that upon entry to the forecast area at more southern latitudes the wind field should display lesser radial extent than at the exit point as many of the storms were in transition or all ready had transitioned to a post tropical system.
Average wind extent changes from entry point to exit point by quadrant
This table shows the average increase or decrease (expressed as a percentage change) in radial extent of each threshold wind in each quadrant during the storms’ presence in the forecast area. Almost universally the data show a significant increase in wind field extent for each threshold value at the exit point when compared to the entry point. Detailed statistics are available by requesting the full report from the Canadian Hurricane Centre.
From the table it is clear that there is significant increase in extent for all quadrants with the greatest increases occurring in the SW and NW quadrants except for hurricane force winds in the SW which showed a significant contraction. However, the counts for hurricane wind cases are very low and not sufficient for a reliable sampling. The larger changes found in the NW and SW quadrants may be partly explained by the transitioning process where expanding pressure fields as well as increased interactions with extratropical features such as high pressure to the north or west can lead to increases in the gradients in these areas.
Tropical Cyclone quadrants were then simplified by combining into two semicircles made up of NE/SE quadrants for the eastern semicircle and SW/NW quadrants for the western semicircle. The table here shows the average radial ranges of each threshold wind range in each semicircle. The rightmost column shows the changes in the ranges of each threshold wind, by semicircle, between the entry and exit positions. Greatest increases in wind field extent are indicated for the western semicircle for all threshold values except hurricane force winds. It is possible that at least some of the increase in the western semicircle is due to not only an expanding pressure gradient associated with the storm as it transitions to post tropical but also the potential for more interactions with extratropical features that can further tighten the gradients. A graphical schematic of these wind-field differences between entry and exit points is shown below the table.
Average wind extents by semicircle and changes from entry to exit points
|Entry Point Average Wind Extent||West Semicircle||East Semicircle||Exit Point Average Wind Extent||West Semicircle||East Semicircle||Change In Wind Field Extent (W/E)|
Composite average wind field extents from entry to exit points
Composited average wind extents by quadrant from the entry to the exit points. In the entry point, the left quadrants have a more condensed wind field and the right quadrants extend out more. In the exit point, all quadrants have expanded considerably with a slightly larger wind field in the right quadrants
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