Tropical Cyclone Nanauk a threat to Oman; Hurricane Cristina Forms in Eastern Pacific

Oman is nervously watching Tropical Cyclone Nanauk (also called Tropical Cyclone Two), a tropical storm with 65 mph winds that is moving west-northwest at 6 mph across the Arabian Sea. Nanauk is over some of the warmest ocean waters on the planet, 31 - 32°C (88 - 90°F). Very warm waters extend to great depth beneath the storm, giving it a Tropical Cyclone Heat Potential (TCHP) of 80 - 120 kJ/cm^2, the type of heat energy that is often associated with rapid intensification. However, Nanauk lies at the southern edge of a large area of dry air coming off the deserts of the Middle East, which is interfering with development. In addition, Nanauk is on the northern edge of the advancing Southwest Monsoon, and strong upper-level winds out of the east associated with the monsoon are bringing high wind shear of 20 - 25 knots, disrupting the circulation.


Figure 1. Morning satellite image of Tropical Cyclone Nanauk over the Arabian Sea.

Forecast for Nanauk
Nanauk is expected to continue moving west-northwest towards Oman the remainder of the week, which will bring the storm into an area with dryer air but lower wind shear. It is difficult to predict how these two competing influences might affect the storm. As a result, the track and intensity forecasts are very divergent. The European model dissipates Nanauk by Wednesday, while the GFS model keeps the storm strong, until weakening occurs shortly before landfall in Oman near 21 UTC on Saturday. Given the storm's ability to fight off high wind shear thus far, I am inclined to go with the GFS forecast of a weakening tropical storm at landfall. Tropical cyclones typically weaken rapidly as they approach the coast of Oman, due to very dry air over the Middle East getting sucked into their circulation.


Figure 2. Progress of the Southwest Monsoon in India in 2014 (blue line and white lines), compared to average (red dashed lines.) The monsoon is running about 4 - 11 days behind schedule, which has allowed Tropical Cyclone Nanauk room to form in the Arabian Sea. Image credit: India Meteorological Department.

The Monsoon and India
The North Indian Ocean has two tropical cyclone seasons--one in May and June before the Southwest Monsoon arrives, and one in October - November after the Monsoon has departed. Ordinary tropical cyclones typically do not form during the monsoon, but huge "monsoon depressions" that fill nearly the entire Bay of Bengal with sustained winds of 30 - 35 mph occasionally form during the monsoon. Nanauk formed just at the leading edge of the advancing monsoon, which is running 4 -11 days behind this year. Nanauk is sapping much of the energy of the monsoon today, which is much less active than it was early in the week. The monsoon is vital to the well-being of India, since the farm sector accounts for 14% of India's nearly $2 trillion economy, and half of India's farmland lacks access to irrigation. The likely development of El Niño this year is of concern for agriculture in India, since El Niño tends to cut down on the monsoon's rains. All of India's great famines since the late 1800s have come in years when the monsoon rains failed during El Niño events.

Record heat scorching India and Nepal
India, Nepal, Pakistan, and Bangladesh typically experience their hottest weather in May and June, just before the arrival of the cooling rains of the monsoon. As reported by wunderground's weather historian Christopher C. Burt in his latest blog post, India has seen extreme heat for the past week, which has led to electricty shortages and riots. At New Delhi’s Palam Airport, the temperature reached 47.8°C (118.0°F) on June 8th, their 2nd hottest temperature ever measured. Agra hit a blistering 47.3° (117.1°F) on June 10th, and 48.6°C (119.5°F) was reported from Ganganagar on June 8th, the warmest reading so far in the country in 2014. In Nepal, the temperature peaked at 45.2°C (113.4°F) at Dipayal, just short of the all-time national record for any month of 46.4°C (115.5°F) set at Dhanghadi on June 16, 1995. Europe has also seen record-breaking June temperatures this week, with Germany hitting its second highest temperature ever recorded in June, 37.9°C (100.2°F) on June 9th in Ihringen.

Cristina becomes a hurricane in the Eastern Pacific
The Eastern Pacific's second hurricane of 2014 is here, as Hurricane Cristina intensified overnight into a Category 1 storm with 75 mph winds. Satellite loops show that Cristina has ingested some dry air and has now leveled off in intensity. Cristina is headed away from Mexico, and it is unlikely that any watches or warnings will be required for this storm.

The usual formation date for the second hurricane of the Eastern Pacific season is July 14, so we are over a month ahead of usual for hurricanes in 2014. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes. NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 22, is calling for an active season, with around 17 named storms, 9 hurricanes, and 4.5 major hurricanes. This year is shaping up to be an El Niño year, and El Niño conditions typically increase the sea surface temperatures and decrease the vertical wind shear over the tropical Eastern Pacific, favoring the development of more and stronger tropical cyclones.


Figure 3. Latest satellite image of Cristina off the Pacific coast of Mexico.

Quiet in the Atlantic
There are no tropical cyclone threat areas in the Atlantic to discuss today, and none of the reliable models for forecasting tropical cyclone genesis is predicting development over the coming five days. The GFS model continues to predict that about 6 - 9 days from now the upper level winds over the Western Caribbean will relax and low-level moisture will build, potentially allowing a tropical disturbance with heavy rains to develop there. However, the European model keeps the wind shear high over the Western Caribbean early next week, so any development in the region remains in doubt.

Jeff Masters