Tropical weather analysis - July 14, 2012
Tropical Storm Emilia is hanging on. As of the most recent NHC advisory, the following was posted on the storm:
Wind: 50 mph, with higher gusts
Location: 15.5°N 132.9°W
Movement: W at 15 mph
Pressure: 997 mb
Category: Tropical storm
Although passage over briefly warmer waters helped to reinvigorate the convection over the last 12-24 hours, Emilia is finally showing signs of a consistent weakening trend. The SHIPS thinks the system is now over water temperatures of 24.5C, and that was as of 18z. Current convective trends would certainly lend some validation to that claim. SSMIS data from several hours ago indicated that the lower- and middle-tropospheric circulations were becoming decoupled. Dvorak numbers are correspondingly beginning to plummet.
Figure 1. Latest infrared satellite image of Tropical Storm Emilia. Image credit: NOAA
Time is running out for Emilia. It continues to move through a very dry airmass, and westerly shear is forecast to increase on Tuesday. This should decapitate whatever is left of the remnant low pressure area by that time.
Emilia continues to move westward south of the subtropical high. This general motion is expected to continue throughout the remainder of the forecast period. The models continue to suggest the possibility of a more south of west motion as the system moves into the central Pacific, but I am having a hard time seeing such a motion. My forecast track will thus not commit to such a sharp southward bend.
5-day intensity forecast
INITIAL 07/14 2100Z 45 KT 50 MPH
12 hour 07/15 0600Z 35 KT 40 MPH
24 hour 07/15 1800Z 30 KT 35 MPH...POST-TROP/REMNANT LOW
36 hour 07/16 0600Z 30 KT 35 MPH...POST-TROP/REMNANT LOW
48 hour 07/16 1800Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
72 hour 07/17 1800Z 20 KT 25 MPH...POST-TROP/REMNANT LOW
96 hour 07/18 1800Z 20 KT 25 MPH...POST-TROP/REMNANT LOW
120 hour 07/19 1800Z...DISSIPATED
5-day track forecast
Figure 2. My 5-day forecast track for Emilia.
Hurricane Fabio has reached Category 2 strength. I mentioned yesterday that it had a chance to achieve such an accolade, but this was a little later in the game than I had anticipated. Regardless, the following was posted on the storm in the special advisory just released from the National Hurricane Center:
Wind: 105 mph, with higher gusts
Location: 16.4°N 115.4°W
Movement: WNW at 9 mph
Pressure: 972 mb
Category: 2 (Saffir-Simpson Hurricane Scale)
The hurricane has a remarkable satellite appearance, with earlier microwave data suggesting a large eye with a well-defined eyewall. Since that time, convection has increased in both coverage and intensity around the cloud-filled eye.
Figure 3. Latest infrared satellite image of Hurricane Fabio. Image credit: NOAA
There is still some northeasterly shear over the system, but it does not look as strong as in recent days. Fabio has probably peaked in intensity, given that it will soon traverse the 26C isotherm. However, it is interesting to note that the last few Eastern Pacific tropical cyclones have taken full advantage of warm waters, so who knows what Fabio has in store in the next few hours. In any case, Fabio should soon begin to weaken as underlying sea surface temperatures cool. By Monday, areal water temperatures decline sharply, and Fabio is expected to respond by rapidly deteriorating. The cyclone is forecast to become a remnant low in about four days, though it could occur a little sooner, especially if vertical shear increases over the hurricane at longer ranges. For now my intensity forecast mirrors that of the National Hurricane Center.
Water vapor imagery and real-time steering analyses suggest that the ridge to the north of the hurricane is weakening with the approach of a trough over the western United States. However, the imagery also suggests that this weakness is very slight, and the ridge is expected to only slowly deamplify. There is still some disagreement amongst the various model members as to how soon Fabio will turn, but in general they have come into better agreement today. I continue to favor the gradual -- rather than rapid -- northward turn I have indicated in previous forecasts. High-level moisture from Fabio's mid-level vorticity maximum is still expected to reach southern California on Thursday, leaving the low-level center far behind.
5-day intensity forecast
INITIAL 07/15 0000Z 90 KT 105 MPH
12 hour 07/15 0600Z 85 KT 100 MPH
24 hour 07/16 1800Z 75 KT 85 MPH
36 hour 07/17 0600Z 65 KT 75 MPH
48 hour 07/18 1800Z 55 KT 65 MPH
72 hour 07/19 1800Z 35 KT 40 MPH
96 hour 07/20 1800Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
120 hour 07/21 1800Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
5-day track forecast
Figure 4. My 5-day forecast track for Fabio.