Tropical weather analysis - July 10, 2012
Persistent Daniel remains a hurricane as of the latest NHC advisory:
Wind: 75 mph, with higher gusts
Location: 15.4°N 132.2°W
Movement: W at 17 mph
Pressure: 992 mb
Category: 1 (Saffir-Simpson Hurricane Scale)
The hurricane remains well-organized considering it is moving over sea surface temperatures of 24C. Daniel continues to generate deep convection, especially to north and the east. This is confirmed by a recent SSMI microwave overpass, which captured the inner core of the circulation quite well.
Figure 1. Latest infrared satellite image of Hurricane Daniel. Image credit: NOAA
Although Daniel remains in a low shear environment, a very dry airmass and cool water temperatures are expected to bring about weakening and eventual dissipation of the hurricane. In addition, the GFS and the GFS-based SHIPS algorithm foresee an abrupt increase in northwesterly shear in about 48 hours. Daniel is likely to drop back down to a tropical storm soon. Most of the models lose the circulation several hundred miles south of the Big Island on Friday the 13th. So do I.
There has been little change to the track philosophy with Daniel. It is being steered westward by a strong mid-level ridge. This ridge is already expanding westward ahead of the hurricane, and a continuation of this general pattern is expected throughout the remainder of the cyclone's existence.
My forecast track remains similar to the 12z ECMWF and that of the National Hurricane Center.
5-day intensity forecast
INITIAL 07/10 0300Z 65 KT 75 MPH
12 hour 07/10 1200Z 55 KT 65 MPH
24 hour 07/11 0000Z 45 KT 50 MPH
36 hour 07/11 1200Z 40 KT 45 MPH
48 hour 07/12 0000Z 30 KT 35 MPH
72 hour 07/13 0000Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
96 hour 07/14 0000Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
120 hour 07/15 0000Z...DISSIPATED
5-day track forecast
Figure 2. My 5-day forecast track for Daniel.
As expected, Emilia has reached major hurricane strength. The latest NHC advisory had this to say about the hurricane:
Wind: 120 mph, with higher gusts
Location: 13.3°N 112.2°W
Movement: WNW at 14 mph
Pressure: 959 mb
Category: 3 (Saffir-Simpson Hurricane Scale)
Emilia is a small but powerful hurricane. The eye has recently become cloud filled, but this is probably just a hiccup in the internal organization.
Figure 3. Latest infrared satellite image of Hurricane Emilia. Image credit: NOAA
Upper-tropospheric outflow remains well-defined, particularly to the north and west where a small upper low moving westward from Baja California is enhancing outflow. However, the hurricane appears to be undergoing some easterly shear, which was confirmed by recent microwave data showing an eyewall that was open to the northeast. A look at 850-200 mb wind shear analyses from UW-CIMSS shows that the anticyclone that was following Emilia has become displaced a few hundred miles to the east. Current trends on water vapor imagery provide some support for this idea. However, the shear does not appear strong enough to penetrate the inner core and cause weakening. Strengthening is still forecast, though it is uncertain how much longer Emilia can keep up the current pace of rapid intensification. Inner core fluctuations, a fancy way of saying eyewall replacement cycle, frequently occur with particularly intense hurricanes like Emilia. These cycles are extremely difficult to predict, however. Interestingly, the very same microwave pass alluded to earlier suggested that an outer band was forming outside the western eyewall, possibly the signal to an eyewall replacement cycle. Satellite images also reveal an increasingly distorted and gradually shrinking eye. However, the outer core does not yet appear to be strengthening, so I am going to assume Emilia is temporarily holding off on an eyewall replacement cycle. After 24 hours, changes to the inner core structure and then cooler waters are expected to bring about a weakening of the hurricane. However, Emilia is expected to remain a viable tropical cyclone throughout the forecast period.
Emilia is expected to continue moving generally toward the west-northwest, with a gradual westward bend near the end of the forecast period as the hurricane weakens and comes underneath the lower-tropospheric easterlies. A mid-level weakness will probably be present in the semipermanent Pacific subtropical high by then, so if Emilia is stronger than predicted at days four and five, it could come within range of the Hawaiian Islands after making the westward turn. For this reason, interests there should continue to remain vigilant of this hurricane. If Emilia did impact Hawaii, it would likely be no more than a tropical depression, and more likely a remnant low. However, tropical cyclones of any kind directly impacting Hawaii is rare in and of itself, which makes this possibility so significant. Aside from heavy rainfall, Emilia would likely not produce any weather out of the ordinary.
5-day intensity forecast
INITIAL 07/10 0300Z 105 KT 120 MPH
12 hour 07/10 1200Z 110 KT 130 MPH
24 hour 07/11 0000Z 115 KT 135 MPH
36 hour 07/11 1200Z 115 KT 135 MPH
48 hour 07/12 0000Z 100 KT 115 MPH
72 hour 07/13 0000Z 85 KT 100 MPH
96 hour 07/14 0000Z 65 KT 75 MPH
120 hour 07/15 0000Z 40 KT 45 MPH
5-day track forecast
Figure 4. My 5-day forecast track for Emilia.
An area of disturbed weather has developed several hundred miles south of Acapulco. Satellite and scatterometer data suggests that this low remains disorganized. However, assuming Emilia doesn't interfere, conditions appear favorable for gradual development as the low moves slowly west-northwest parallel to the Mexican coast. Long-range model projections of the synoptic pattern suggest that there will be a trough over California capable of turning the system northward toward southern Baja. However, there is considerable uncertainty in such long-range forecasts. In the meantime, locally heavy rainfall may impact portions of the southern Mexico coast over the next day or so as the disturbance slowly consolidates.
Probability of development in 48 hours: 40%