IBTrACS version 4

[benjimin]

As of March 2019, IBTRACS version 3 is obsolete. Should update code to point at new dataset, check still tests ok, and also consider vendoring, i.e., bundling the data for distribution with tcrm.

[benjimin]

Note WMO version of IBTracs has been deprecated.

[KayShelton]

Running TCRM v3.0.1 with IBTrACS V4 falls over due to 1986226N30276 26/08/1986 12:00:00 longitude being beyond the maximum longitude in the grid. _lonLat function in DataProcess.py fails due to dependency on sampleGrid function in Utilities/grid.Py. The call to np.searchsorted on line 259 in grid.py requires a clip/clamp to keep values in range.

[KayShelton]

To properly handle the IBTrACS V4 dataset, the dataProcessing code requires tweaking. Positions are generally supplied every 3 hours in the new IBTrACS, but pressure data is only available at 3 hourly intervals for the most recent seasons.

When calculating the pressure rates, the _pressureRate function in DataProcess needs to be parsed only the non-missing pressures and associated dt between these obs, or the entire function needs to be re-designed.

I have implemented a workaround for this in my code (I am testing the downstream impact on the generated tracks at present), which I'd be happy to share, but I feel it may be a little clunky.