95L Little Threat; TD 21E a Long-Range Threat to Mexico's Pacific Coast

An area of disturbed weather (95L) just north of the Virgin Islands is headed northwest at 10 to 15 mph. Satellite loops show that 95L has large, sloppy surface circulation and moderate amount of heavy thunderstorm activity that is mostly disconnected from the center of the storm by high wind shear of 20 - 30 knots. Water vapor satellite images show that 95L has dry air to its west that is likely interfering with development. Sea Surface Temperatures (SSTs) are warm, about 29°C. The 8 am EDT Thursday run of the SHIPS model predicted that wind shear would remain a high 20 - 30 knots through Saturday night, then increase to 30 - 50 knots beginning on Sunday. These high wind shear values make development conditions marginal through Saturday, then almost impossible beginning on Sunday. None of our three reliable models for predicting tropical cyclone genesis predict development of 95L over the next five days. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day development odds of 10%. The only land area at risk from 95L is Bermuda.


Figure 1. MODIS satellite image of Invest 95L to the northeast of Puerto Rico on Wednesday afternoon October 29, 2014. The surface circulation center was exposed to view by high wind shear. Image credit: NASA.

Arabian Sea's Tropical Cyclone Nilofar getting ripped up by wind shear
In the Arabian Sea between India and Africa, Cyclone Nilofar has been shredded by high wind shear of 40 - 50 knots. and was a tropical storm with just 50 mph winds at 10 am EDT Thursday. Even higher levels of wind shear, combined with very dry air from the deserts of the Middle East, should cause Nilofar to dissipate on Friday. Nilofar's remnants will be capable of bringing 1 - 2" of rain over the weekend to the Pakistan/India border region, according to the 2 am EDT Thursday run of the HWRF model.


Figure 2. MODIS satellite image of Tropical Cyclone Nilofar in the Arabian Sea on Thursday morning, October 30, 2014. At the time, Nilofar was a tropical storm with 55 mph winds, and the low-level circulation had been exposed to view by high wind shear. Image credit: NASA.

Tropical Storm Vance forms in the Eastern Pacific
Tropical Storm Vance formed in the Eastern Pacific on Thursday afternoon. Satellite images show that Vance is in the organizing stages, with a small area of heavy thunderstorms, some solidifying low-level spiral bands, and a Central Dense Overcast (CDO) of high cirrus clouds, characteristic of intensifying tropical storms. The storm is over warm SSTs, near 29°C, but some dry air and moderate wind shear are slowing development. By Saturday, these issues should relent, allowing intensification into a Category 1 hurricane by Sunday. The storm's heaviest rains will remain well offshore from Mexico over the next four days, but our two top models for predicting hurricane tracks--the GFS and European models--forecast that Vance will get pulled to the northeast by a trough of low pressure early next week, and make landfall in Mainland Mexico northwest of Puerto Vallarta on Tuesday night. The 8 am EDT Thursday run of the SHIPS model predicted that wind shear would remain low, 5 - 10 knots, though Monday, then ramp up significantly on Monday night and Tuesday as Vance gets caught up in the trough of low pressure that will sling it into Mexico. The higher wind shear should be able to significantly weaken Vance before landfall, making heavy rain the primary threat.

Hurricane expert Steve Gregory has more on the tropics in a Thursday afternoon post.

Jeff Masters