indian ocean Intense Tropical Cyclone Amara

[Vorticity0123]

After quite a lull in overall TC activity, a new tropical depression has formed in the south Indian Ocean. (Though the JTWC has only issued a TCFA of the system) The system is forecast to move toward the west and then recurve slowly to the south while still located to the north of La Reunion.

 

 

In the long term, the cyclone is forecast to continue moving slowly toward the south, as high pressure to the south of the system is blocking the system from recurving quickly into the westerlies.

 

Below is the GFS forecast of the system:

 

GFS T+120

 

GFS T+180

 

As stated above, an almost erratic motion is forecast for the system. Also note that there is another TC forecast to spin up to the east of TD 02. This system will likely slowly move toward the south during its lifetime.

 

Currently, the system is becoming better organized, with shallow convection, as well as some banding, occuring in the westen semicircle. However, the system does seem to be under influence of some easterly shear, as seen in the IR loop from the NHC. Below is IR imagery of the cyclone.

 

 

Shear analysis of CIMSS shows that the system has an anticyclone positioned directly overhead, which partially denies the possible easterly wind shear.

 

 

The cyclone is located directly under the anticyclone with 10-20 knots of shear.

 

This could become quite an intense TC, I'll post more information about the intensity later today or tomorrow.

 

Sources:

http://www.meteo.fr/temps/domtom/La_Reunion/meteoreunion2/

http://www.wetterzentrale.de/topkarten/fsavnet.html

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

http://www.ssd.noaa.gov/PS/TROP/floaters/93S/flash-vis-short.html

http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=indian&sat=wm5∏=shr&zoom=&time=

Edited December 16, 2013 by Vorticity0123

[Somerset Squall]

Yep, it seems the South Indian Ocean cyclone season is starting, about on time too. This should become the first named storm of the Southwest Indian Ocean 2013-14 season pretty soon I would've thought (Alessia was an Australian region cyclone), banding features are becoming more prominant and there is a healthy amount of convection centrally.

EDIT: Now named Amara by MeteoFrance.

Edited December 16, 2013 by Somerset Squall

[Somerset Squall]

JTWC have issued their first warning on Amara, indicating winds have reached 35kts. They are forecasting some strengthening as the storm heads west-southwest over the coming few days:

 

Latest image of Amara:

 

 

[Vorticity0123]

JTWC have issued their first warning on Amara, indicating winds have reached 35kts. They are forecasting some strengthening as the storm heads west-southwest over the coming few days:

 

The RSMC is somewhat more aggressive on Amara, bringing it to hurricane status in about 48 hours.

 

 

Reading through the JTWC forecast, it appears that Ocean Heat Content (OHC) will be the main inhibiting factor for Amara. Especially when it starts to move more slowly in about 5 days time.

 

The AVNO model forecasts Amara to reach about 65 knots in 4 days time:

 

 

Meanwhile, the GFS (as shown in my first post) is also pretty aggressive on bringing the cyclone to hurricane status.

 

Concluding, it seems certain that Amara will intensify, but the rate at which it occurs is yet to be seen, as RSMC la Reunion and JTWC are in some disagreement regarding the intensification rate.

 

And finally, a nice CIMSS MIMIC TPW loop, showing nicely the amount of moisture that is being transported within the cyclone.

Also visible is a tropical low currently spinning up to the east of Amara.

 

Sources:

http://tropic.ssec.wisc.edu/real-time/mimic-tpw/indo/main.html

http://www.meteo.fr/temps/domtom/La_Reunion/meteoreunion2/

http://www.wetterzentrale.de/topkarten/fsavnet.html

http://www.ral.ucar.edu/guidance/realtime/plots/southernhemisphere/2014/sh932014/

Edited December 16, 2013 by Vorticity0123

[Coast]

Tropical Storm AMARA: Probability of tropical storm winds to 120 hours lead

 

 

Tropical Cyclone AMARA-13 can have a low humanitarian impact based on the Maximum sustained wind speed and the affected population and their vulnerability.

 

Tropical Cyclone Tropical Storm (maximum wind speed of 111 km/h)

on 16/12/2013 18:00 UTC

 

Population affected by Category 1 (120 km/h) wind speeds or higher is 0

 

Extreme Rain

 

Potential rainfall is calculated based on rainfall observed by several microwave satellite sensors.

 

Storm surge

 

The tropical cyclone did not reach sufficient strength to cause significant storm surge.

 

 

http://www.gdacs.org/report.aspx?eventtype=TC&eventid=41924

[Vorticity0123]

It seems like RSMC la Reunion was the most accurate with their intensity forecast. Visible imagery, along with satellite intensity estimates from CIMSS, show that Amara has intensified steadily since yesterday.

 

CIMSS ADT intensity estimates are already at 55 knots, while JTWC analyzed the system at 35 knots from last advisory.

 

 

Meanwhile, AMSU and SATCON estimates are already at hurricane strength (76 and 69 kt respectively). This suggests that RI could be occuring right now. 

 

(Somewhat ragged) Rainbow imagery shows Amara consists of a ball of convection with some banding features to the north and the south of the system. To me it seems like a high-end tropical storm.

 

 

Overall, the structure seems to be well-enough organized for continued intensification, as it continues to move west-southwestward.

 

Above example once again illustrates the difficulity to forecast periods of RI occuring. 

 

What is also quite interesting, is that the coldest SSTS will be reached in 2 days time (26 deg. C). Thereafter, SSTS will be on the rise again (if the forecast verifies). This is because there is a warm tongue extending to the southeast of Madagascar. As long as the cyclone doesn't meander too much (upwelling), it could maintain its intensity for quite a long time (more than 7 days), if other conditions remain favorable.

 

 

 

Sources:

http://www.ssd.noaa.gov/PS/TROP/floaters/03S/imagery/rb0-lalo.jpg

http://tropic.ssec.wisc.edu/#

http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/13121706/2.html

[Coast]

[Somerset Squall]

Amara has continued to strengthen, and JTWC have raised the intensity to 50kts. Marginal ocean heat content may be a factor in limiting intensity gains in the near term, but the upper level conditions are favourable. Warmer waters near La Reunion and Mauritius, which Amara could move over in a few days time, would support further intensification.

The steering environment is complex, as two ridges are competing for steering influence, which is causing Amara to move slowly. The ridge to the southeast should win out, allowing Amara to accelerate to the west-southwest soon.

[Coast]

Amara now being chased by Bruce:

 

[Somerset Squall]

Amara has strengthened considerably overnight, with winds now at 80kts according to JTWC. The compact system has developed an eye, which isn't all that well defined yet, but it is definitely a sign of things to come. With low shear and good outflow expected to persist over the next day or two, and Amara's small size, Amara could continue to ramp up quickly.

[Somerset Squall]

Amara has continued to rapidly intensify. Winds are up to 100kts according to JTWC, making Amara a cat 3 on the SS scale. The eye is becoming better defined, embedded in the central dense overcast, which is small but solid. Shear is low, and outflow is excellent, with a channel now venting in both a poleward and equatorward direction. These dual outflow channels, along with Amara's small size, could facilitate further rapid strengthening over the next 24hrs, before the upper level environment begins to deteriorate. JTWC expect a peak of 130kts, which would make Amara the strongest storm in the Southwest Indian Ocean, in their estimates, since Edzani in 2010.

 

 

 

[Somerset Squall]

Now classified as an "Intense Tropical Cyclone" by MeteoFrance, with an estimated pressure of 944mb. Certainly an impressive first cyclone of the Southwest Indian Ocean season!

Edited December 19, 2013 by Somerset Squall

[Somerset Squall]

Amara peaked at 115kts (SS scale cat 4) between JTWC advisories:

 

0313121818 168S 699E 1000313121818 168S 699E 1000313121818 168S 699E 1000313121900 170S 692E 1150313121900 170S 692E 1150313121900 170S 692E 1150313121906 174S 683E 1050313121906 174S 683E 1050313121906 174S 683E 105

 

The cyclone has since weakened, as the eye has lost definition, although the central dense overcast remains quite solid. Winds are down to 105kts according to JTWC. They explain this weakening is due to an unexpected decrease in outflow, which has caused the cloud top temperatures to warm and the convection to  weaken. They no longer forecasted further strengthening, and expect Amara to slowly weaken over the next couple days, with faster weakening after that as shear increases.

 

Amara continues to move fairly slowly southwestwards but is expected to turn south then southeast as a trough weakens the steering ridge to the southeast. This will steer Amara very near or directly over the island of Rodrigues, bringing high winds and rain here, despite Amara being forecasted to be a weaker cyclone at this time. A turn back to the west is then expected as the ridge builds back towards the south of Amara, though the timing and occurence of this turn is still uncertain.

[Coast]

 

NASA's TRMM satellite saw heavy rainfall was happening in Tropical Cyclone Amara on December 16, and still occurring on December 19, although it moved from east to southeast. Warnings are already in effect for Mauritius' Rodrigues Island.

 

NASA's Tropical Rainfall Measuring Mission or TRMM satellite can measure rainfall rates from space, and that's what it has been doing over Tropical Cyclone Amara since it was born. On Dec. 16, at 2043 UTC/3:43 p.m. EST TRMM data showed scattered bands of moderate to heavy rain falling at a rate of over 76.9 mm/3 inches per hour spiraling into Amara's center. Cloud tops reached 13 km/8 miles high near the center and eastern side.

 

On Dec. 19 at 0441 UTC, the Naval Research Laboratory in Washington, D.C. combined TRMM satellite rainfall data with a visible image of Amara's clouds from Japan's METEO-7 satellite to provide a complete picture of the storm. The image revealed that the heaviest rain was falling southeast of the center at 1.6 inches/40 mm per hour. By 0900 UTC/4 a.m. EST, Tropical Cyclone Amara's maximum sustained winds were near 105 knots/120.8 mph/194.5 kph, making it hurricane-strength. Amara was still about 740 nautical miles east-northeast of La Reunion Island, centered near 17.2 south latitude and 68.3 east longitude. Amara does, however, threaten Rodrigues Island. The Mauritius Meteorological Service or MMS has already put a cyclone class 2 warning in effect for Rodrigues Island. The island is part of the Republic of Mauritius and is located about 350 miles/560 kilometers east of Mauritius.

 

 

 

http://phys.org/news/2013-12-nasa-heavy-tropical-cyclone-amara.html#jCp

[Somerset Squall]

Amara has managed to strengthen once more to 115kts, cat 4 on SS scale. The central dense overcast feature has deepened and the eye has remained well defined.

[Somerset Squall]

Amara's eye is just passing to the east of Rodrigues island. However, the island is still being battered by damaging winds and torrential rains from dangerous Amara.

[Somerset Squall]

Intense Amara has strengthened still further overnight, and winds have reached a whopping 130kts, high end cat 4 on the SS scale. Westerly shear is increasing, so Amara is expected to weaken later today.

[Somerset Squall]

Amara has indeed weakened as it curves southeastwards. The eye is no longer visible on satellite imagery, and the central dense overcast has become irregular, distorted by shear. Winds have fallen to 110kts, cat 3 on the SS scale. Further weakening can be expected.

[Somerset Squall]

Amara has weakened to 90kts, cat 2 on the SS scale. The LLCC is becoming partially exposed from the deep convection due to shear.

 

Tracks of both Amara and Bruce, showing how close Amara got to Rodrigues a couple days ago:

 

 

 

[Somerset Squall]

Amara is falling apart, very quickly. Convection has largely dissipated, and winds have dropped to 60kts. However, without convection, Amara's circulation should wind down quickly, and with the strong shear currently affecting Amara, persistant convection does not look likely to return.

[Somerset Squall]

Amara is gone. Convection didn't come back, and JTWC issued their last advsory this afternoon. In fact, it looks like Amara's remains are being absorbed by TC Bruce to the east.