Hurricanes Harvey, Irma and Jose: Gulf of & Caribbean 2017. Generalities These 3 large hurricanes have occupied a lot of media attention because of the damage they have wrought - and because it happened to the USA. (Similar damage and more loss of life have occurred to Bangladesh and to the Philippines and eastern Asia by typhoons.) Appearing in the (Figure 1) at much the same time, but a little later as shown by its alphabetical order, another hurricane, Katia, hit Mexico but weakened on landfall with less damage, landfall occurring a day after the more catastrophic 8.1 earthquake off Mexico’s west coast. Harvey and Irma caused massive damage from winds and flooding. Jose looked threatening to mainland USA but veered northward into the Atlantic (Figure 9), presumably latching onto the warm Gulf Stream, as did the later Ophelia. 2010 was a similarly busy season.

Figure 1: Gulf of Mexico and Caribbean hurricanes, 2017 & 2010. [via Twitter, Gia Milani]

The formation of hurricanes is much as stated for Cyclone Pam (chapter 4) - although the interacting Atlantic Ocean and Caribbean currents cause complexity. Tropical storms regularly initiate in the eastern Atlantic, often between the west African coast and west of Cape Verde (16°N 24°W) – which incidentally happens to be a geological “hotspot”, warming the ocean when active. It’s also about where the southbound Canary Current (figure 2) turns west to become the North Atlantic Equatorial Current (NAEC) increasingly being warmed by tropical Sun. The warmed ocean increases evaporation, often enough to produce tropical storms. Due to the Coriolis force, such storms spin anti-clockwise in the northern hemisphere but clockwise in the southern. If warm water is in a storm’s path, the storm will increase perhaps to hurricane level, defined as spinning faster than 119 km.hr-1 for a category 1.

Storms follow warmed currents because the winds direct them along this path of lower pressure, feeding further moisture into the storm. Consequently, hurricanes tend to fade when they make significant landfall because their moisture supply is cut.

1 This wasn’t the case with Harvey and Irma. Because these enormous storms dumped massive amounts of rainfall onto (warm) land, they formed their own inland sea, to help the storms invade into southern mainland USA. Of course, they eventually ran out of surface water and stopped advancing inland.

Figure 2: Ocean Currents (Wikipedia: Ocean Current)

One prevailing westward-flowing surface current here is the North Atlantic Equatorial Current - although it flows well north of the Equator. It flows at about 9 to13 km per day, much slower than hurricanes track. For example, Irma tracked at about 460 km/day (19 km.hr-1) from Aug31 to Sep6. The NAEC interacts with the Gulf of Mexico and the Gulf Stream along the north of Cuba.

The other Atlantic current is the South Equatorial Current. Despite its name, one part splits to flow into the northern hemisphere, then into the Gulf of Mexico and eventually adding its warmth to the Gulf Stream. Because it travels closer to the Equator, it will be warmer than the NAEC until later in the northern summer. Consequently, it will be the favoured path of earlier storms such as Harvey into the Gulf of Mexico, whereas the later storms will largely follow the then warmer NAEC to the Caribbean.

A complicating factor: The paths of the NAEC and the SAEC pass over the Mid- Atlantic Ridge (Figure 13, chapter 2), which diverges about 3 cm.yr-1 but as with most things geological, irregularly in bursts registering as earthquakes. Shallow earthquakes at diverging plate boundaries indicate the release, or imminent release, of hot undersea lava to warm* the ocean, and so, the timing, number and size of these quakes along the Mid-Atlantic Ridge influences a storm’s path. [*Each volume of lava is approximately equal in heat capacity to an equal volume of water; each cubic metre of lava at 1200C raises the temperature of 600 times that volume of water ie 600m3, by 2C.]

Specifics Igor & Julia & Karl (all Sept2010) did not make US landfall2. Igor & Julia both passed over the Mid-Atlantic Ridge which had twin ‘quakes 04Aug2010 (figure 3)

2 followed by 11Sep2010. Karl, 13 to 18 Sep 2101, apparently arrived via the SAEC, passing south of those quakes but intensifying in the tropically warmed Gulf.

Figure 3: 2010 seismic data *1 (Period 20Jul10 to 20Sep10, Mag>2.5) No Date Mag Depth, km Latitude Longitude 1 04Aug2010 4.8 10 22.7°N 44.9°W 2 04Aug2010 4.4 10 19.1°N 46.1°W 3 11Sep2010 4.7 10 15.3°N 45.8°W

The tectonic boundary shown running from northern South America, around past northern Hispaniola then into Mexico, is the boundary between the North American Plate (in the north) and the Caribbean Plate. As can be seen, it is particularly active around Hispaniola, but as it is a (conservative) strike-slip boundary, it generates only

Figure 4: 2010 Track (Weather Underground2)

3 little heat, via friction, especially relative to a diverging one (Chapter 2) and these low Mag quakes have no effect on storms and their data are not considered here.

The 10km depth shown is a nominal value for a shallow quake, especially if it is far from a seismic station such as those near the Mid-Atlantic Ridge. Apparently, the length of time after this that hot magma is exuded varies with location, and the accuracy of measurement of the depth.

Figure 5: 2010 Hurricanes Julia & Karl Track2

4 Once they passed the Mid-Atlantic Ridge, the two more northerly hurricanes, Igor and Julia, became attracted by the Gulf Stream’s warmth.

Figure 6: 2017 seismic data (Period 01Apr17 to 26Oct17, only Mag>4.5 shown)

Time GMT Latitude Longitude Depth km Mag 2017-10-03 Z 13.46 -49.33 10 5.7 2017-08-31 Z 13.29 -49.39 10 4.8 2017-08-02 Z 13.49 -49.34 10 5.3 2017-07-27 Z 13.40 -49.33 10 6.0 (Selected from Table 1) The earliest 3 of these co-located quakes fed into Harvey, Irma and Jose. [The 10Sep was too late to affect these hurricanes but is included here to illustrate that spot’s activity.]

The Gulf of Mexico’s hurricanes also result from tropical storms riding the South Equatorial Current (SEC) into the Gulf, until the Current runs into the Yucatan Peninsula. If the storm’s diameter is sufficiently large, it may pick up extra moisture from a sufficiently warm Gulf to cross the peninsula into it, becoming hurricanes, as Harvey (Aug2017), Katia (Sep2017) and Karl (Sep2010) did.

Hurricanes Harvey, Irma and Jose all initially intensified near the same location, a little west – ie downstream and downwind - of the strong seismic activity (13°, -49°)

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Figure 7: Track2 (18Aug17 to 03Sep17.) Date Time Lat Lon Wind Pressure Storm Type Category Potential Tropical Aug 18 15:00 GMT 13.1° -55.1° 35 mph 1008 mb - Cyclone Aug 26 00:00 GMT 27.8° -96.8° 130 mph 941 mb Hurricane 4

Figure 8: 2017 Track2 Aug 31 15:00 GMT 16.4° -30.3° 50 mph 1004 mb Tropical Storm Sep 05 11:45 GMT 16.7° -57.7° 175 mph 929 mb Hurricane 5

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Figure 9: 2017 track2 Sep 06 15:00 GMT 12.3° -39.1° 40 mph 1008 mb Tropical Storm - Sep 08 14:00 GMT 16.2° -56.9° 150 mph 942 mb Hurricane 4

Hurricane Ophelia3 (09 to 16 October 2017, max Category 3). Although less powerful than the Caribbean/Gulf of Mexico hurricanes, it was the first for decades to reach as far east as the UK.

Figure 10: 2017 Track2

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Ophelia resulted from a tropical depression (09Oct17) that had latched onto the warm Gulf Stream, itself passing over the active northern Mid-Atlantic Ridge, gaining extra warmth from recent large - in size and number - seismic activity (figure 6) and Table 1. The extra ocean warmth had even been noted in the popular press4.

time latitude longitude depth mag 2017-10-19T22:23:27.610Z 7.4006 -35.7032 10 5.2 2017-10-19T06:45:01.850Z 33.7862 -38.8445 10 5.1 2017-10-08T14:14:13.890Z 10.6525 -41.3479 10 5 2017-10-03T20:39:04.740Z 13.4587 -49.3322 10 5.7 2017-09-27T04:09:52.430Z 28.7234 -43.5388 10 5 2017-09-27T03:15:55.670Z 28.6061 -43.5406 10 4.7 2017-09-22T22:56:19.560Z 7.4851 -35.8191 10 4.8 2017-09-20T15:26:08.060Z 43.6321 -28.7481 10 4.6 2017-09-08T15:59:27.500Z 25.2517 -45.1832 10 4.8 2017-09-07T20:27:25.090Z 25.3649 -45.3734 10 4.6 2017-08-31T14:55:36.470Z 13.287 -49.3878 10 4.8 2017-08-30T14:22:20.150Z 40.0478 -29.7553 10 4.7 2017-08-30T14:20:05.390Z 39.8949 -29.6094 10 5.3 2017-08-30T14:19:14.680Z 40.0099 -29.4168 10 5 2017-08-30T14:09:31.660Z 39.8606 -29.3943 10 4.6 2017-08-18T19:24:20.700Z 41.0473 -29.1907 10 4.6 2017-08-15T07:35:30.000Z 36.1537 -34.0008 10 4.6 2017-08-14T17:04:28.640Z 36.1337 -33.8996 10 4.8 2017-08-10T06:46:00.300Z 41.4157 -29.3325 10 4.6 2017-08-10T04:28:03.400Z 41.5742 -29.4081 10 5 2017-08-02T00:16:12.150Z 13.4905 -49.344 10 5.3 2017-07-27T17:53:24.610Z 13.396 -49.3259 10 6 2017-06-30T01:34:58.140Z 33.7413 -38.5445 10 5.9 2017-06-13T12:06:17.440Z 35.3336 -35.8849 10 4.6 2017-05-19T01:54:21.380Z 40.8042 -28.7253 10 4.7 2017-05-06T00:21:02.090Z 22.8684 -45.0138 10 4.8 2017-05-05T23:56:49.180Z 22.8744 -44.9841 10 4.9 2017-05-05T23:55:54.860Z 23.0308 -45.0567 10 4.8 2017-05-01T13:48:05.680Z 43.6248 -28.7847 10 4.8 2017-04-29T00:31:36.310Z 25.9829 -45.2131 10 4.6 2017-04-29T00:16:54.340Z 25.537 -45.3129 10 4.6 2017-04-27T03:45:54.490Z 8.4821 -39.5793 10 4.9 2017-04-14T15:11:09.740Z 15.4376 -46.8641 10 4.6 Table 1: 2017 Mid-Atlantic Ridge activity 01Apr17 to 26Oct17 Mag>4.5, Area 45°N -20° to 5°N -52°

Southern Australia 2016 [The date is corrected from the 2017 date stated incorrectly in the first version of this Chapter.] Closer to home, on 29 September 2016 a giant storm hit South Australia, and embarrassingly wiped out the whole state’s electricity supply for at least 6 hours but for many days in some places.

The storm developed from a Low, with perhaps the lowest pressure recorded in the vicinity, in the cold Southern Ocean about two thousand kilometres south of the

8 continent. Lows develop over warm areas, and this just happened to sit over the South-Eastern Indian (or Western Indian-Antarctic Ridge). Such Lows, often producing rain on southern Australia, can be seen to appear commonly in this otherwise cold ocean – as “Antarctic” suggests.

The intense Low developed in the otherwise cold Southern Ocean, more than 1000km south of Western Australia. From the weather maps (figures 8), the pressure dropped from about 1004 hPa to 964 hPa (27Sep16, 58S 128E) and this Low travelled rapidly to hit mainland South Australia 29Sep16.

Q: Lows form over warm areas. Then how does a warm patch develop in a frigid Southern Ocean?

A: The heat to cause the Low was produced by lava release from the divergent Western-Indian Antarctic Ridge. This release was originally signalled near 50S 126E by rumblings of 4·5 and 4·4 on 15th and 17th July 2016 at depths of 15 and 13 km, then two quakes separated by two minutes of Mag 5·5, and 5·8, depth 10km, 25Jul16. Apparently, it took some further weeks for the lava to actually break through and emerge to heat the ocean, producing the Low.

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Figure 11: Australia Weather Maps, 27, 28 & 29 Sep2016.5

time latitude longitude depth mag 2016-10-13 T08:33:00.920Z -50.5396 112.0412 10 4.6 2016-08-09 T00:18:01.350Z -49.281 123.2657 10 4.5 2016-08-07 T01:41:48.150Z -49.5222 125.9549 10 4.4 2016-07-25 T09:00:28.390Z -49.4245 126.3706 10 5.5 2016-07-25 T08:58:30.790Z -49.4848 126.2657 10 5.8 2016-07-18 T15:59:59.180Z -49.5484 125.109 13.42 4.4 2016-07-15 T17:09:27.590Z -49.2941 127.3394 15.03 4.5 2016-07-05 T16:17:37.780Z -50.3469 114.0534 10 4 Table 2: 2016 Southern Ocean Seismic Activity

[The 25Jul16 activity listed here below from USGS as two quakes are given as a single Mag 6·1 quake by Geosciences Australia.]

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Figure 12: Seismic Activity south of Australia, 05Jul16 to 13Oct16 Area: 34°S - 137°E to 53°S – 106°E, Mag>2·5.

Many lesser Magnitude quakes form along this Ridge to produce smaller Lows, but 5·8 - alternatively 6·1 - was large, especially so for a divergent boundary, indicating a large lava release. (The Richter Mag scale is logarithmic.)

Summary and Observations Meteorologists forecast conditions such as storms; they are produced by the Sun’s heat on Earth’s irregular surface. Frustrating such forecasts, heat released from unseen undersea volcanic activity can increase the intensity of storms if they pass above at the right time. Such activity can be seen to have affected the weather countless times simply by observing the Lows suddenly develop on weather maps above undersea tectonic boundaries, particularly divergent ones.

Because it is situated under the north-bound Gulf Stream, it is expected that the Mid- Atlantic Ridge’s lava-exuding divergence activity will influence Europe’s weather in an irregular manner.

1 Seismic data are from US Geological Survey, USGS, website https://earthquake.usgs.gov/earthquakes/ Searches can be conducted with user-determined parameters, such as time period, area, Mag, depth, etc.

2 Storm data are from Weather Underground’s website https://www.wunderground.com/hurricane/atlantic/ Searches can be conducted using hurricane name. Their data are much more extensive than shown here.

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3 https://en.wikipedia.org/wiki/Hurricane_Ophelia_(2017)

4 https://www.washingtonpost.com/news/capital-weather-gang/wp/2017/10/15/ophelia-strongest- eastern-atlantic-hurricane-on-record-roars-toward-ireland/?utm_term=.eed3ffa4a9e6

5 http://www.bom.gov.au/australia/charts/archive/index.shtml

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