Tropical Cyclone Imelda

[Somerset Squall]

Tropical Cyclone 21S has formed around 200 miles south of Diego Garcia, in the central South Indian Ocean. This ends a five and a half week period without a cyclone in this basin, which is unusual. No tropical cyclone activity was observed in March, which is uncommon. 21S has sustained winds of 35kts. The cyclone is expected to strengthen as it heads just south of west over the coming days, as the current moderate shear abates and joins the good outflow and warm waters to promote intensification. Ridging to the south is expected to guide 21S on the westerly track until it begins to break down by day 4/5 which will cause a poleward turn for 21S at this stage, probably well before the approach to Madagascar. JTWC expect a peak of 100kts, and MeteoFrance are similarly aggressive in their intensity forecast. Moderate shear will slow strengthening at first, but as it eases, the other environmental parameters are very favourable for robust strengthening.

[Somerset Squall]

21S has become Tropical Cyclone Imelda, with sustained winds now at 40kts. Imelda has strengthened slowly due to moderate shear, which is slowly abating. Banding features are becoming more prominant, and convection is building nearer the LLC. Further intensification is expected as Imelda continues westwards over the next day or two. Imelda is then expected to turn quite sharply southward as a trough breaks down the steering ridge to the south beyond this time.

[Somerset Squall]

Imelda continues to strengthen. Intensity is at 50kts this morning. Strong banding flanks a central dense overcast which is beginning to show signs of an eye feature.

[Coast]

Tropical Storm IMELDA: Probability of Cat 1 or above winds to 120 hours lead

[Coast]

Tropical Cyclone Imelda is churning in the open waters of the Southern Indian Ocean and NASA's Aqua satellite captured a visible image of the storm that showed bands of thunderstorms were wrapping tightly into the center of circulation.

On Friday, April 5, Imelda was a low pressure area designated "93S" that appeared ripe for development on NASA satellite imagery. On Saturday, April 6, 93S consolidated and became a tropical depression. Now, that depression has strengthened into a tropical storm, and is expected to continue strengthening to hurricane-force.

When NASA's Tropical Rainfall Measuring Mission (TRMM) satellite passed over Imelda on April 8 at 0408 UTC (12:08 a.m. EDT) it revealed low-level bands of thunderstorms over the western semicircle, while northeast of the center, the bands of thunderstorms were fragmented and weak. Since then, those bands have organized.

NASA's Aqua satellite passed over the low pressure area on April 8 at 0605 UTC (2:05 a.m. EDT) and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument captured a visible image of Tropical Cyclone Imelda in the Southern Indian Ocean. MODIS imagery showed a large band of thunderstorms wrapping into the center of circulation from the south. That band of thunderstorms has been slowly consolidating over the 12 hours previous.

On April 8 at 0900 UTC (5 a.m. EDT) Imelda had maximum sustained winds near 40 knots (46.0 mph/74.0 kph). Imelda was centered near 11.0 south latitude and 64.7 east longitude, about 490 nautical miles west-southwest of Diego Garcia and moving to the west at 12 knots (13.8 mph/22.2 kph). Diego Garcia is an atoll in the shape of a footprint that is made up of coral. It is located south of the equator in the central Indian Ocean, in British Indian Ocean Territory.

Forecasters at the Joint Typhoon Warning Center (JTWC) noted that the easterly vertical wind shear has relaxed slightly to 10 to 15 knots (11.5 to 17.2 mph/18.5 to 27.8 kph). JTWC forecasters expect Imelda to continue tracking west southwestward for the next two days and strengthen.

http://www.nasa.gov/mission_pages/hurricanes/archives/2013/h2013_Imelda.html

[Coast]

[Somerset Squall]

Imelda has grown in size significantly today and intensified further. Sustained winds are now at 60kts. Imelda continues to head westwards but the southward turn is expected soon. Conditions remain favourable for further strengthening as outflow remains good, shear low and waters warm.

[Somerset Squall]

Imelda has popped out a large eye from the central dense overcast. Imelda has started to slow, indicating that the cyclone is nearing the western extent of the ridge steering it. Sustained winds are now at 70kts, and Imelda should continue to strengthen over the next 36-48 hrs.

[Somerset Squall]

Imelda has become a cat 2 on the Saffir Simpson scale, with sustained winds now at 85kts. The cyclone retains a solid central dense overcast with a shrinking eye embedded in it. Impressive banding features continue to flank Imelda. Some more strengthening is expected.

[Somerset Squall]

Imelda has unexpectedly weakened today. Shear has risen, eroding the convection from the LLC. The eye has long gone, and the LLC is now partially exposed. Intensity has fallen to 55kts. Imelda is now moving to the southeast. The cyclone is expected to find lower shear again and therefore does have the opportunity to restrengthen a little in the 24-60hr time frame.

[Somerset Squall]

Imelda is in trouble. Winds are down to 35kts currently, and convection is lacking. Waters are warm and shear low to moderate, but troughing is causing subsidence and dry air over the LLC. Imelda is no longer expected to re-strengthen, and instead should dissipate in a day or two, unless the trough moves away from Imelda, which is not considered likely at this time.

[Somerset Squall]

Imelda has surprised us again, and has strengthened to 50kts. Convection has blossomed over the LLC, and banding features have developed again. Imelda could strengthen a little more as outflow has improved over the last 12hrs. Longer term, Imelda should weaken again as shear rises on the southeasterly track.

[Somerset Squall]

Imelda continues to strengthen in it's new found favourable environment. An eye has once again developed, and sustained winds are now at 75kts (10kts less than Imelda's first peak). Imelda is near it's second peak I would've have thought as shear values are much higher to the south. Imelda is expected to continue southeast in the near term as a near equatorial ridge steers the cyclone, but Imelda should turn westwards thereafter as ridging to the south gains control of steering influence.

 

[Somerset Squall]

Imelda has weakened to 55kts. Convection is being sheared away from the LLC as shear has risen to moderate to high levels. Shear is expected to persist and further weaken Imelda over the next day or two.