NASA Gets a Final Look at Tropical Cyclone Ockhi’s Rainfall

Tropical Cyclone Ockhi is quickly weakening in the Arabian Sea and is expected to dissipate on Dec. 6 when it makes landfall in northwestern India. The Global Precipitation Measurement mission or GPM core satellite passed over Ockhi and looked at its rainfall as wind shear was affecting the storm.

On Dec. 4, GPM found rain falling at a rate of over 62 mm (2.44 inches) per hour in storms northeast of the center. On the western side storms rainfall was occurring at a rate of over 60 mm (2.27 inches) per hour. Credits: NASA/JAXA, Hal Pierce

On Dec. 2, Ockhi became the first tropical cyclone of the year to form in the Arabian Sea. Fortunately for India the tropical cyclone remained off India’s southwestern coast. Ockhi intensified to the equivalent of a category 3 hurricane on the Saffir-Simpson hurricane wind scale before it started to weaken. Vertical wind shear caused Ockhi to weaken as the tropical cyclone started moving north-northeastward toward India’s Gulf of Khambhat.

NASA’s GPM Core Observatory satellite passed over Tropical Cyclone Ockhi on Dec. 4 at 1:16 a.m. EST (0616 UTC). GPM is a joint mission between NASA and the Japanese space agency JAXA.

The rainfall coverage was derived from data collected by GPM’s Microwave Imager (GMI) and Dual-Frequency Precipitation Radar (DPR) instruments. Those data showed that very heavy rainfall was being produced by powerful storms northwest of Ockhi’s eye. Wind shear was already pushing the strongest storms away from the center of circulation.

GPM’s GMI found rain falling at a rate of over 62 mm (2.44 inches) per hour in those storms. GPM’s radar (DPR Ku Band) sliced through the western side of the tropical cyclone. DPR found that powerful storms on that side of Ockhi were dropping precipitation at a rate of over 60 mm (2.27 inches) per hour.

At NASA’s Goddard Space Flight Center in Greenbelt, Md. a 3-D view of tropical cyclone Ockhi was created using GPM’s radar (DPR Ku Band) data. The 3-D image showed a slice through the western side of the tropical cyclone and revealed storm tops reaching heights above 16 km (9.92 miles). The 3-D cross-section by GPM’s DPR revealed that many radar reflectivity values were greater than 50 dBZ in downpours on the western side of the tropical cyclone.

The Joint Typhoon Warning Center (JTWC) issued their final bulletin on Ockhi on Dec. 5 at 4 a.m. EST (0900 UTC). At that time, Ockhi’s maximum sustained winds were near 45 knots (52 mph/83 kph) and weakening. Ockhi was centered near 8.7 degrees north latitude and 70.8 degrees east longitude. That’s about 444 nautical miles south-southeast of Karachi, Pakistan. Ockhi has tracked north-northeastward at 9 knots (10.3 mph/16.6 kph).

JWTC noted at that time “Animated multispectral satellite imagery depicts a rapidly-decaying, fully-exposed, broad low-level circulation center with limited deep convection sheared well northeast of the low-level center due to strong (40-50 knots) southerly vertical wind shear.” The storm was also becoming extra-tropical.

JTWC predicts that Ockhi will continue to weaken. Ockhi is expected to become a remnant low when it makes landfall near the Gulf of Khambhat early on Dec. 6.

Source: NASA

Flood Summary

Last updated: December 4, 2017
Event
Cyclone Ockhi, Sri Lanka and India, November to December 2017
Date
November 29, 2017
Type
Flash flood
Cause
Extreme rainfall

Locations

A - Galle (Sri Lanka)
B - Kalutara (Sri Lanka)
C - Matara (Sri Lanka)
D - Monaragala (Sri Lanka)
E - Hambanthota (Sri Lanka)
F - Kandy (Sri Lanka)
G - Nuwaraeliya (Sri Lanka)
H - Rathnapura (Sri Lanka)
I - Badulla (Sri Lanka)
J - Gampaha (Sri Lanka)
K - Puttalam (Sri Lanka)
L - Kegalle (Sri Lanka)
M - Matale (Sri Lanka)
N - Kurunagala (Sri Lanka)
O - Colombo (Sri Lanka)
P - Anuradapura (Sri Lanka)
Q - Thiruvananthapuram, Kerala (India)
R - Kanyakumari, Tamil Nadu (India)
S - Minicoy Island, Lakshadweep, India (India)

Magnitude

Rainfall level
66 mm in 24 hours
Deraniyagala, Kegalle District, Sri Lanka - December 2 to December 3, 2017
Rainfall level
121 mm in 24 hours
Baddegama, Galle District, Sri Lanka - November 30 to December 1, 2017
Rainfall level
86.2 mm in 24 hours
Putupaula, Kalutara District, Sri Lanka - November 30 to December 1, 2017
Rainfall level
99.7 mm in 24 hours
Pitabeddara, Matara District, Sri Lanka - November 30 to December 1, 2017
Rainfall level
168.40 mm in 24 hours
Putupaula, Kalutara District, Sri Lanka - November 29 to November 30, 2017
Rainfall level
111.9 mm in 24 hours
Baddegama, Galle District, Sri Lanka - November 29 to November 30, 2017
River level
4.31 metres
Gin Ganga at Baddegama, Sri Lanka - December 3 to December 3, 2017
Major flood level is 5 m
River level
6.7 metres
Nilwala Ganga at Panadugama, Sri Lanka - December 2 to December 2, 2017
Major flood level 6.50 m
Rainfall level
107 mm in 24 hours
Nagapattinam, Tamil Nadu, India - December 3 to December 4, 2017
Rainfall level
195 mm in 24 hours
Nagapattinam, Tamil Nadu, India - December 2 to December 3, 2017
Rainfall level
158.1 mm in 24 hours
Pondicherry, India - December 1 to December 2, 2017
Rainfall level
119.5 mm in 24 hours
Kanyakumari, Tamil Nadu, India - December 1 to December 2, 2017
Rainfall level
169 mm in 24 hours
Minicoy, Lakshadweep, India - December 1 to December 2, 2017

Damages

Fatalities
13 people
Sri Lanka - November 29 to December 3, 2017
Galle (8), Matara (1), Badulla (3) and Gampaha (1)
Buildings destroyed
694 buildings
Sri Lanka - November 29 to December 3, 2017
423 of them in Kalutara, 155 in Galle, others in Matara, Badulla, Colombo and elsewhere.
Evacuated
5,435
Sri Lanka - November 29 to December 3, 2017
Evacuated
6,581
Kerala, India - December 2 to December 4, 2017
Buildings destroyed
63 buildings
Kerala, India - December 2 to December 4, 2017
Fatalities
19 people
Kerala, India - December 2 to December 4, 2017

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