Hurricane Irma Got Relegated

17 03 2018

Dale C. S. Destin |

Hurricane Irma was relegated from being tied for the second strongest Atlantic hurricane, in terms of wind speed, to being tied for being the third strongest. This is according to the final report on the system issued last week by the U.S. National Hurricane Center (USNHC). The USNHC, in its post-mortem report, lowered Irma’s maximum sustained winds from 185 mph to 180 mph.

VIIRS SATELLITE IMAGE OF HURRICANE IRMA WHEN IT WAS AT ITS PEAK INTENSITY AND MADE LANDFALL ON BARBUDA AT 0535 UTC 6 SEPTEMBER.

VIIRS Satellite Image of  Hurricane Irma When it was at its Peak Intensity and Made Landfall on Barbuda at 0535 UTC (1:35 am) 6 September, 2017.

The downgrade of Irma, by 5 knots (5.75 mph), is relatively negligible; however, from the record book standpoint, it is notable. And looking at the raw data, the USNHC may have still been generous with the peak winds of 180 mph – it could have been lowered further.

There are some other notable things gleamed from the report that I would like to share. A report I would recommend persons to read.

Recall that many persons blamed Irma on climate change, something that I and others continue to debunk? It turned out that Irma’s strength had very little to do with warm sea surface temperatures – the link that is being made to climate change, and more to do with low wind shear and available atmospheric moisture, according to the USNHC report – not climate change.

USNHC has confirmed what we already recognized – Irma was a very small hurricane. Her hurricane force winds extended only 24 km (15 miles) from the centre. On average, the hurricane force winds from a hurricane extends out 64 km (40 miles). Her small size saved Antigua from similar type destruction to what occurred in 1995 from Hurricane Luis.

Along parts of the track of Irma, the effect of the winds on the sea was reminiscent of a tsunami. For example, in Puerto Piloto, the sea retreated offshore by up to 12 metres (39 feet) due to the force of the southerly winds on the eastern side of Irma’s circulation. No doubt similar would have happened for parts of Barbuda and elsewhere.

Irma's Storm-Surge as Recroded by Our Station at River Road, Codrington, Barbuda

Irma’s Storm-Surge as Recorded by Our Tide Station at River Road, Codrington, Barbuda

For Barbuda, the was a tsunami-like surge of 2.5 metres (9.3 feet) measured by our tide gauge at River Road, Codrington, which is on the southern side of the island. It is likely that the surge generated by on the north side was higher. These surges inundated significant portions of Codrington and the island as a whole, which is very flat. At least half of the island lies within 25 feet of mean sea level. The Codrington Lagoon remains breached from the massive surges and waves created by Irma.

In addition to the tsunami-like surge, there were monster waves as high as 8 metres (26 feet) caused by Irma. Such large waves on top of the high surge would have caused seawater to inundate areas well inland, causing serious erosion and saltwater intrusion into aquifers and agricultural lands.

Also confirmed was the fact that the ECMWF was by far the best performing model with respect to the track forecast. However, all the models were left wanting with respect to the forecast of intensity.

In weeks we will have the first set of forecast for the upcoming hurricane season, stay tuned for those.

Don’t forget to take our weather survey, which will help us to better communicate the weather to you: Weather Survey.

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