Updated Tuesday, 5,30pm: A cyclone warning remains in place for Nhulunbuy to the Queensland border, including Groote Eylandt, Numbulwar, Ngukurr, Bulman, Port Roper, and Port McArthur.
The watch for areas east of Beswick has been cancelled.
The BoM said that heavy rain was likely to develop across parts of the Arnhem and Carpentaria Districts from Wednesday extending into Daly district on Thursday. Flooding of low lying areas and rising rivers are predicted.
Northern Territory Emergency Services has advised residents in Alyangula that they should shelter indoors as winds and rain start later on Tuesday.
The GEMCO Mess will be open to GEMCO staff and Alyangula residents from midnight on Tuesday.
Shelters are also open at Angurugu School Trade Training Centre; Umbakumba School Trade Training Centre; Milyakburra Cyclone Shelter.
The shelter at Numbulwar School will open from midnight on Tuesday.
Residents who are not able to safely shelter at home have been advised to take emergency kits with them to the shelters and put into place arrangements for care of any pets.
All but essential travel in the warning area should now cease.
Updated Tuesday, 10.33am: A watch area for ex-tropical cyclone Tiffany now extends inland to areas east of Beswick but not including the community.
The Bureau of Meteorology said that the watch alert for Beswick, Barunga and Mataranka had been cancelled.
A cyclone warning remains in place for Nhulunbuy to the Queensland border, including Groote Eylandt, Numbulwar, Port Roper, and Port McArthur.
Gales were expected to develop about Groote Eylandt from early Wednesday morning and between Nhulunbuy and the Queensland border later that day depending on how the weather system tracks.
The destructive core of the system is expected to cross the coast between Cape Shield and Nathan River on Wednesday afternoon with wind gusts up to 140 km/h.
The BoM said that gales with wind gusts to 100 km/h may extend inland to areas to the east of Beswick overnight on Wednesday as the cyclone moves inland.
A storm tide between the Queensland border and Cape Shield, including Groote Eylandt, is expected as the centre of the cyclone crosses the coast, with significantly higher-than-normal tides.
The BoM has predicted damaging waves and dangerous flooding between the Queensland border and Cape Shield including Groote Eylandt.
Heavy rain and flooding have been forecast in the Arnhem and Carpentaria Districts from Wednesday.
Updated Tuesday: 7.10 am: A cyclone warning has been issued for Nhulunbuy to Queensland border, including Groote Eylandt, Numbulwar, Port Roper, and Port McArthur.
Inland areas extending west to Barunga and Mataranka have been included in a watch zone.
The cyclone, with destructive gusts up to 140 km/h, was expected to cross the coast between Cape Shield and Nathan River on Wednesday afternoon.
Gales with gusts up to 100 km/h may extend west to Barunga and Mataranka overnight on Wednesday as the cyclone moves inland.
Heavy rain was likely to develop across parts of the Arnhem and Carpentaria Districts from Wednesday and was expected to cause flooding of low lying areas and river rises.
People in the warning area should be ready for a cyclone and wet and windy conditions by finalising home preparations and knowing where to shelter.
Communities under a cyclone watch should consider what action to take if the threat increases and activate their household plans.
The area of a warning for severe thunderstorms is now around Boorooloola stretching to the Queensland border.
The storms are likely to produce damaging winds and heavy rainfall that may lead to flash flooding in the warning area over the next several hours.
UPDATED Tuesday 6am: People on Groote Eylandt have been advised to activate their household cyclone plan as ex-Tropical Cyclone Tiffany was expected to re-intensify today into a Category 2 cyclone.
A cyclone watch remains in place for Nhulunbuy to the Queensland border, including Numbalwar, Port Roper, and Port McArthur.
The Bureau of Meteorology said that as of 3.30am (CST) the tropical low had sustained winds near the centre of 55 kilometres per hour with wind gusts to 85 kilometres per hour.
It was about 175 kilometres west southwest of Coen and 40 kilometres north of Pormpuraaw and moving 18 kilometers an hour. On Wednesday, it will move towards the eastern Northern Territory coast where category 2 tropical cyclone impacts are possible.
Groote Eylandt can expect gales developing on Wednesday morning to increase to destructive winds with gusts of up to 140 km/h as the centre of the cyclone approached.
Gales are not expected on the Northern Territory mainland within the next 24 hours, however they could develop later on Wednesday between Nhulunbuy and the Territory/Queensland border.
Heavy rain is likely across parts of the Arnhem and Carpentaria Districts from Wednesday and is expected to cause flooding of low-lying areas and rising rivers. The main impact for Katherine is likely to be rainfall.
A severe severe thunderstorm warning has also been issued in the western Gulf Country, on the southern periphery of Ex-Tropical Cyclone Tiffany.
The BoM said that severe thunderstorms are likely to produce damaging winds and heavy rainfall that may lead to flash flooding in the warning area over the next several hours from 4.11am CST. Locations which may be affected include Wollogorang and Booroloola.
EARLIER: A cyclone watch has been declared for Nhulunbuy to the Queensland border, including Groote Eylandt.
Tropical Cyclone Tiffany made landfall in Far North Queensland earlier today and is currently located southeast of Coen.
Tiffany has weakened to a category one system and is expected to weaken further as it moves across the peninsula before reaching the Gulf of Carpentaria on Tuesday morning.
It is expected to cross the NT at Groote Eylandt on Wednesday.
"On Wednesday it will move towards the eastern Northern Territory coast where a severe tropical cyclone impact is possible," a statement from the BOM reads.
Flooding is likely in the Carpentaria coastal rivers, and the Bureau of Meteorology has also issued a flood watch for the region.
Northern Territory Police, Fire and Emergency Services have stood up the Emergency Operations Centre to coordinate the preparation for and response to this event.
Regional Controller, Assistant Commissioner Janelle Tonkin said there were no plans to evacuate residents of Groote Eylandt.
"We are keeping a close eye on the possible tracks of this storm, and our local emergency management teams have activated their plans and are making the necessary preparations to see their communities through this event," she said.
"We are confident at this stage that we will not have to evacuate anybody from Groote Eylandt, the cyclone structures there are designed to withstand Category 3 storms. However, anyone who wishes to leave should do so early."
Duty Forecaster at the BOM, Sally Cutter, said the Big Rivers region was set to feel the impacts of Tiffany later this week.
"At this stage it's looking like it's possibly reaching a cat 3 before it crosses Groote Eylandt, and then weakening as it moves over land," Ms Cutter said.
"But there's certainly going to be very heavy falls associated with the circulation as it moves inland."
Ms Cutter said Katherine will likely see rain on Friday and into the weekend, with areas east of Katherine feeling the impacts sooner.
"The damaging winds are probably not going to get as far as Katherine, but they might get a little bit inland. So, Numbulwar, Ngukkur, those areas probably more likely to be impacted by those damaging wind gusts," she said.
"The main impact is going to be the rainfall for Katherine."
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