Strengthening Cristobal Headed Out to Sea; 97L and Gulf of Mexico Worth Watching

Tropical Storm Cristobal continues to dump heavy rains over the Central and Southeast Bahamas and Turks and Caicos Islands as the storm heads slowly north-northeastwards out to sea. Satellite loops show that Cristobal is struggling with wind shear, with a center of circulation that is completely exposed to view, and all the heavy thunderstorms pushed to the south and east sides of the center. The shear is expected to relax by Wednesday as a trough of low pressure captures the storm and accelerates it to the northeast, out to sea. Cristobal will likely be intensifying into a Category 1 hurricane as it brushes Bermuda on Wednesday, and the 11 am EDT Monday Wind Probability Forecast from NHC gave that island a 41% chance of experiencing tropical storm force winds of 39+ mph.


Figure 1. MODIS true-color image of Tropical Storm Cristobal over the Southeast Bahamas at 15:55 UTC (11:55 am EDT) on August 24, 2014. At the time, Cristobal had top winds of 45 mph Image credit: NASA.

Keeping an eye on 97L headed towards the Lesser Antilles
A tropical wave (Invest 97L) was near 12°N, 40°W on Monday morning, midway between the coast of Africa and the Lesser Antilles Islands, and was headed west to west-northwest at about 15 mph. Satellite loops show the wave has a modest amount of spin but only a small amount of heavy thunderstorms. Water vapor satellite images and the Saharan Air Layer analysis show that 97L is located in a dry environment, which is keeping development slow. Wind shear was a moderate 10 - 20 knots, and the 8 am EDT Monday run of the SHIPS model predicted that wind shear would mostly stay in the moderate range for the next five days, which should allow some slow development. Sea Surface Temperatures are near 27.5°C, which is warm enough to allow some slow development. The wave should arrive in the Lesser Antilles Islands by Friday, according to the Monday morning runs of the GFS and European models. One of the 00Z Monday runs of the three reliable computer models for predicting tropical storm formation, the UKMET model, showed some weak development of 97L by Friday as it passes just north of the northernmost Lesser Antilles Islands. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day development odds of 0% and 30%, respectively.

Keeping an eye on the Gulf of Mexico
In the Gulf of Mexico, a weak cold front is kicking up some heavy thunderstorms in the Louisiana coastal waters. This activity will spread to the Texas coastal waters by Wednesday. With wind shear a moderate 10 - 20 knots, we should monitor this area for development. About 1/3 of the 20 members of the 06Z Monday GFS model ensemble showed some development in the Gulf on Thursday or Friday. (The GFS ensemble is a set of 20 runs of the GFS model done at lower resolution with slightly different initial conditions to generate an uncertainty "plume" of model runs.) The preferred track of the system was to the west towards Texas.


Figure 2. MODIS true-color image of Hurricane Marie in the Eastern Pacific taken at 20:40 UTC (4:40 pm EDT) on August 24, 2014. At the time, Marie was a Category 5 storm with 160 mph winds. Image credit: NASA.

Mighty Hurricane Marie generating huge waves in Eastern Pacific
Hurricane Marie exploded into the Eastern Pacific's first Category 5 hurricane in four years on Sunday, maintaining Category 5 winds of 160 mph for six hours before an eyewall replacement cycle weakened the storm slightly. The hurricane was still a very powerful Category 4 storm with 145 mph winds on Monday morning, though satellite loops showed a steady degradation of the cloud pattern, with the eyewall cloud tops warming and the areal coverage of the strongest thunderstorms decreasing. The storm is headed northwest over cooler waters and into drier air, and will not affect any land areas. However, Marie's tropical storm-force winds cover a huge area of ocean, up to 310 miles from the center, and these winds are generating massive swells that are bringing high surf to the shores of Mexico's Baja Peninsula. These swells will pound the shores of Southern California Tuesday through Thursday. A High Surf Advisory is in effect for Los Angeles, where waves of 10 - 15 feet will potentially cause structural damage to piers and beachside property as well as significant beach erosion. The powerful surf will be accompanied by strong rip currents and long-shore currents, making for very hazardous swimming and surfing conditions. According to NWS in San Diego, Marie's ascension to Category 4 status on August 24 is the earliest in the year the Eastern Pacific has seen its 5th major hurricane since reliable records began in 1949.

You can see a spectacular loop of infrared satellite images of Marie as it intensified into a Category 5 storm on Sunday at the CIMSS University of Wisconsin.

The GOES-West Satellite will be in rapid scan mode over Marie on Monday, and loops will be available at the NOAA/RAMMB website.

The Western Pacific remains quiet, with no new named storms expected to develop over the next five days. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, is currently in a phase that creates sinking air of the Western Pacific. This discourages tropical cyclone formation. By late next week, this suppressed phase of the MJO will likely shift so that tropical storm formation is suppressed over the Atlantic, keeping the traditional peak portion of the Atlantic hurricane season quieter than usual.

Jeff Masters