Published On: Tue, Sep 5th, 2017

Irma now classified as Category 4: A dangerous hurricane

On the twenty-second anniversary of Hurricane Luis, St. Maarten is once more in the eye of the storm as Hurricane Irma approaches. The last update from the National Hurricane Center at 8 p.m. last night described Irma as a dangerous hurricane. Preparations within the warning area should be rushed to completion, forecaster Pasch wrote.

What was the situation at 8 p.m. last night? Irma was located at 16.7 N and 55.0 W. The coordinates of St. Maarten are 18 N and 63 W.

Based on these numbers the storm was last night 144 kilometers south of St. Maarten and 889 kilometers to the east.

The maximum sustained winds measures 220 kilometers per hour and the system moved west at 20 kilometers per hour, suggesting that the center of the storm will be at our islands longitude in around 44 hours; that’s Wednesday afternoon at around 4 p.m.

But this does not mean that we will not experience Irma’s effects sooner, because hurricane-force winds extend up to 65 kilometers from the center of the system and tropical storm-force winds extend outward of the center for 220 kilometers.

The National Hurricane Center described Irma last night as a category 4 hurricane on the Saffir-Simpson hurricane wind scale.

The bad news: additional strengthening is forecast for the next 48 hours.

The hurricane obviously also affects the sea. The combination of a dangerous storm surge and large breaking waves will raise water levels by as much as 6 to 9 feet (roughly 1.80 to 2.75 meter) above normal tide levels along the coast of the extreme northern Leeward Islands within the hurricane warning area and to the north of the center of Irma. Near the coast, the surge will be accompanied by large and destructive waves.

The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded, the National Hurricane Center says. This phenomenon will mainly affect the US Virgin Islands and Puerto Rico, where water could rise between 1 and 6 feet above ground if the peak surge occurs at the time of high tide.

The forecast predicts hurricane force winds within the warning area (that includes St. Maarten) by tonight, preceded by tropical storm conditions.

Irma will also bring lots and lots of rain. The forecast is 3 to 6 inches across the Leeward Islands, with isolated maximums of 10 inches. For the metrics among us: 3 inches is more than 7 centimeter; 10 inches is around 25 centimeter. That’s a lot of water by any standard and the National Hurricane Center points out that this rainfall may cause life-threatening flash floods and mudslides.

Swells generated by Irma will affect the northern Leeward Islands during the next several days. These swells are likely to cause life-threatening surf and rip current conditions.

Last night there were hurricane warnings in effect for St. Maarten, Saba, Statia, St. Barths, Anguilla, Antigua, Barbuda, Montserrat and St. Kitts and Nevis. There were hurricane watches in place for Guadeloupe the British and the US Virgin Islands, Puerto Rico, Vieques and Culebra. A tropical storm warning was also in place for Guadeloupe and a tropical storm watch for Dominica.