Yesterday (day before?), I showed how it takes IKE down to 44MPH (4 days from now). It has not changed its mind:
07Sep08 12Z run
now 24 48 72 96 120 (hours from now)
132 98 50 45 36 26 (predicted mph)
http://www.nhc.noaa.gov/modelsummary.shtml
The “technical summary chart” of NHC still has very strong praise for SHIPS’ intensity predictions. Something isn't clicking for me right now. I was guessing that SHIPS was looking at historical tracks and going from there to intensity predictions, inspired by the tracks shown in a post above. That is NOT at all what it does- it is a tuned multiple regression model. “The predictors for SHIPS include climatology and persistence, atmospheric environmental parameters (e.g., vertical shear, stability, etc.), and oceanic input such as sea surface temperature (SST) and upper-oceanic heat content.” (... much more)
For some reason, SHIPS believes this sucker is going to really get degraded over the next two days.
I would really love it if someone seeing this could give me any explanation that this well respected intensity model is giving such a different solution!
I sure would love to see SHIPS predictions come true, because really, Ike scares me. It probably won't... but why is it so out of line?
Ben Nelson, Floridas state meteorologist, said this is a very complicated situation to forecast. I have heard that hurricanes cool the water. Gustav just went through these waters. Perhaps SHIPS is taking that into account?
Missing the obvious? 24 hours w/ core over or near Cuba land mass?
Statistical Hurricane Intensity Prediction Scheme (SHIPS) Model
The SHIPS model is a statistical-dynamic intensity prediction model. This model was developed using standard multiple regression techniques with climatological, persistence, and numerical model forecasts as predictors. Estimates of future storm intensity are made for 12-hr periods out to 120 hr.
The SHIPS equations were initially developed using data from 49 storms during the period 1982-1992 that were at least 30 nautical miles from land. (The collection of synoptic data for LBAR began in 1989, as did the archive of operational intensity forecasts. Data for selected storms during 1982-88 were available and included in the SHIPS developmental data set.) The SHIPS equations are typically updated each year.
Major changes have been the development of DSHIPS (Decay SHIPS) in 2000 to account for the decay of storms over land, the extension of the forecasts to Day 5 in 2001, the replacement of the simple dry-adiabitic prediction model in 2001 with output from the operational global model (the GFS) for the evaluation of the environmental predictors, and the inclusion of satellite-derived parameters (specifically, cloud top temperatures and oceanic heat content) in 2004.
Unlike earlier versions, the most recent versions of SHIPS have significant skill over climatology, at least out to Day 3.
The primary predictors are:
Current storm intensity;
Day of the year;
Persistence (intensity change in previous 12 hrs);
East-west compontent of storm motion;
Divergence of the wind at 200 mb;
Intensification potential (the difference between the current storm intensity and an estimate of the Maximum Possible Storm Intensity determined from the sea surface temperature);
The vertical shear of the horizontal wind in the 850-200 mb layer;
Average 200 mb temperature;
Average 850 mb vorticity;
Average 500-300 mb layer relative humidity;
Cloud top temperature as measured by the GOES satellite infrared imager channel and
Oceanic heat content inferred from altimetry measurements from polar orbiting satellites.
Vertical wind shear is evaluated for the 850-200 mb layer because most satellite cloud track winds are assigned to those levels. The 500-300 mb relative humidity attempts to estimate the impact of any Saharan Dust Layer propagating across the Atlantic basin, which tends to inhibit storm intensitifaction. Terms 1-5 are evaluated at the initial storm location. All other terms are averaged along the forecast storm track.
Research has shown that the sea surface temperature (SST) alone does not provide a good indication of whether a storm will intensify. (See, for example the SST/Intensity relationships of recent Atlantic tropical cyclones.) However, SST does provide an upper limit to storm intensity. In SHIPS, the Maximum Possible Storm Intensity (MPI) is related to the SST by the equation:
MPI = 55.6 kt + 108.5 kt exp[0.1813 * {SST - 30.0oC)]
Since the SHIPS equations were developed using data from storms that were over water, the SHIPS intensity forecasts are not valid for storms near the coast. In 2000 a new version of the model, called Decay SHIP (DSHP), was introduced. The DSHP is identical to the SHIPS model except, if the cyclone is forecast to cross land, the intensity is reduced accordingly. The DSHIPS model had the smallest errors at all forecast periods during the 2000 Atlantic season.
References: DeMaria, M. and J. Kaplan, 1999: An updated statistical hurricane intensity prediction scheme (SHIPS) for the Atlantic and Eastern North Pacific Basins. Wea. Forecasting, 14, 326-337.
DeMaria, M. et al., 2005: Futher improvements to the Statistical Hurricane Intensity Prediction Scheme (SHIPS). Wea. Forecasting, 20, 531-543.
Relative Skill of the Intensity Guidance Models
These graphs shows the skill of the intensity guidance models for the past two seasons | Note that the skill for intensity is typically much less than that for storm track, and has not improved substantially in recent years.