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Somerset Squall

Severe Tropical Cyclone Nathan

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A tropical low has formed in the Coral Sea. JTWC has issued a tropical cyclone formation alert on the system. 17U is expected to move westwards towards the Cape York Penisula whilst intensifying into a tropical cyclone. The westwards motion is forecast by BOM to cease before the system reaches the coast as the ridge to the south weakens and sends the cyclone back to the east. The timing of this turn is uncertain, as it does depend on the timely arrival of the trough that is forecast to break down the ridge. Conditions look generally favourable for intensification, with the system forecast to become quite intense as it moves back towards the east.

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BOM have upgraded 17U to Tropical Cyclone Nathan, with winds of 40kts. Nathan has developed good convective banding and improved central convection. The outer bands of Nathan are providing heavy rains for the Cape York Peninsula. Nathan is expected to continue to strengthen as it nears the coast, but is still expected to head back eastwards before any landfall can occur.

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Nathan has strengthened to 50kts according to BOM. The cyclone is still under some shear, but this should ease soon allowing for quicker intensification. Nathan is moving northwestwards at the moment but the turn back east should occur in about 24hrs.

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The turn hasn't happened yet, but should soon. Shear continues to impinge on Nathan, placing the majority of the convection to the west over land. Winds remain at 50kts according to BOM. Nathan is still expected to strengthen once it turns east.

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After stalling for another day or so after I posted, Nathan began to move back towards the east. Shear has continued to plague Nathan, and winds are down to 45kts according to BOM and 40kts according to JTWC.

It seems that Nathan could well reverse course yet again soon. The cyclone is currently moving southeastwards as ridging to the north remains in charge of the steering currents. A building ridge to the south could assume steering influence soon, and Nathan is forecast to track south and possibly then back to the west as a result, though this is uncertain.

Due to favourable outflow, Nathan should finally strengthen over the next day or two. It is after which, JTWC and BOM disagree. BOM forecast intensification for the next 4 days, wheras JTWC forecast strengthening for the next 36hrs, followed by weakening as shear drives cool, dry air into Nathan. BOM also mention this as a second possibilty.

Track map from JTWC show Nathan's wandering track so far:

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Nathan has meandered slowly to the south over the last 48hrs, and has changed little in strength due to continued shear. Nathan should soon move out of the weak steering environment and move more quickly westwards towards the Queensland coast. Landfall is expected north of Cairns, near Cape Tribulation. Shear is expected to at last ease off, allowing Nathan to finally strengthen before landfall. Nathan is then expected to cross the Cape York Peninsula, and emerge in the Gulf Of Carpentaria as a weak system, where there is a chance of re intensification.

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Nathan is intensifying in lower shear conditions. Winds are up to 50kts. Convection is now persisting directly over the LLCC, and increasingly well developed banding features are becoming evident. Nathan could rapidly intensify prior to landfall. Both BOM and JTWC forecast Nathan to cross the Cape York Peninsula and then restrengthen in the Gulf Of Carpentaria. It seems wondering, long lived Nathan will be around for a while yet. Of more concern however, is a potentially damaging impact from Nathan on the Cape York Peninsula, particularly if the current strengthening trend persists.

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Forecast track map will be updated shortly. Earlier, BOM was forecasting Nathan to make landfall just north of the township of Cooktown ( pop 2000 ).

The Cooktown weather forecast issued an hour ago factors in the cyclone prognosis

http://archive.today/nB77s

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Nathan continues to intensify, with winds now at 70kts according to BOM. Further intensification, perhaps rapid, is expected, as shear is now very low, waters warm and outflow excellent. The track has shifted slightly north, which puts Cooktown and Cape Flattery more in the firing line from Nathan's small core of what will be quite intense winds and heavy rainfall.

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Nathan continues to intensify, with winds now at 70kts according to BOM. Further intensification, perhaps rapid, is expected, as shear is now very low, waters warm and outflow excellent. The track has shifted slightly north, which puts Cooktown and Cape Flattery more in the firing line from Nathan's small core of what will be quite intense winds and heavy rainfall.

 

After spending around 8 days wandering over Coral Sea waters as a weak tropical storm, tiny and tenacious Nathan has been in the process of rapid development. As Somerset Squall said, conditions have become very favourable for development, which has led to the formation of a circular eye surrounded by a rather small eyewall.

 

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Visible satellite image of Nathan as of 12 UTC, 18 March.

 

The small eyewall of the cyclone is also visible in microwave IR imagery:

 

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MIMIC imagery loop of Nathan (click to animate).

 

On the last few frames, a tiny eyewall shows up, which is quite difficult to discern at a first glance.

 

Given the current state of Nathan, continued rapid intensification seems like a plausible option. Unfortunately, the system is now forecast to make landfall in a few days, but the impact radius seems to be relatively small as given the small size of the inner core of the cyclone.

 

Sources:

http://www.bom.gov.au/products/IDQ65002.shtml

http://www.ssd.noaa.gov/PS/TROP/floaters/18P/18P_floater.html

http://en.wikipedia.org/wiki/2014%E2%80%9315_Australian_region_cyclone_season

http://tropic.ssec.wisc.edu/real-time/mimic-tc/2015_18P/webManager/mainpage.html

http://www.usno.navy.mil/JTWC/

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Nathan's winds are now at 80kts. The cyclone is expected to attain an intensity of 100kts, possibly more before landfall. Nathan is expected to survive the trip over the Cape York Peninsula, and re-intensify in the Gulf Of Carpentaria. The cyclone is then expected to move west-northwest towards the Top End, and make a second landfall. It looks likely Nathan will then emerge over water yet again and move into the NW Australian waters, where again, re-intensifcation is possible. Nathan's taking a trip all the way round Australia it seems, if the forecast verifies!

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Nathan is not far off landfall. Winds are up to 90kts according to JTWC. Nathan will be making landfall in the next couple of hours, just north of Cape Flattery.

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Nathan still looking pretty well organised inland with 1-min sustained winds estimated at 70kts, should emerge back over water later this evening. As Nathan seems to be coping pretty well over land, this means that intensification is likely over the Gulf Of Carpentaria.

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It'll be interesting to see what Nathan has in store for Darwin early next week as it tracks westward over sea just off the Top End coastline. Last night the forecast was for a squally situation with flooding rains but it now appears Nathan will go into ex-tropical mode again before it gets up there.

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Nathan weakened to 35kts before entering the Gulf Of Carpentaria. Nathan is about midway across the Gulf currently, moving quite briskly west-northwestwards. Winds have increased to 40kts. Nathan has some fairly deep convection over the LLCC, and good convective banding. As shear is low and waters very warm, further strengthening appears likely before landfall in the Top End, east of Darwin. Just what happens after that for Nathan is uncertain. What appears likely is that shear may increase, so even if Nathan manages to find water again, it may not fair well.

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Nathan strengthened to 65kts (1 min sustained, JTWC) before making it's second landfall, near Gove, NT. Nathan has weakened slightly over land, to 60kts. The current west-northwesterly trajectory is expected to persist, which will take Nathan back out over water again soon. As shear remains low, Nathan should strengthen again before a trough weakens the ridge to the south, forcing Nathan southwestwards towards a third landfall, currently progged by BOM to be midway between Goulburn Island and Croker Island. After the trough passes, the ridge should restrengthen, sending Nathan on a more westerly track. On this track, Nathan should emerge over water yet again, this time in NW Australian waters. Conditions here appear favourable for yet another episode of re - strengthening.

It appears 12 day old Nathan will be around for some time yet.

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Nathan has made it's third landfall and has since weakened rapidly. Nathan has been declared a remnant low. The remnants of Nathan are still expected to emerge over water in about 24hrs, where some redevelopment is possible. However, based on the fact that Nathan has weakened over land much faster than expected, the system may be too weak to regenerate. In addition, shear is moderate over the far eastern South Indian Ocean, which is another factor arguing against significant redevelopment.

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